Chemistry. Assessment Unit A2 1. assessing. Module 4: Further Organic, Physical and Inorganic Chemistry WEDNESDAY 31 MAY, AFTERNOON

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1 A2.1: : Old Old Spec Jan : Old Spec 469 pages in total. Chemistry TIME 1 hour 30 minutes. Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry WEDNESDAY 31 MAY, AFTERNOON ADVANCED General Certificate of Education 2006 INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all fifteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all five questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Quality of written communication will be assessed in question 11(d)(ii). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

2 Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 Which one of the following always has units? A B C D K w K p ph pk a 2 Methanol is synthesised by reacting carbon monoxide with hydrogen. CO + 2H 2 CH 3 OH H = 91 kj mol 1 A temperature of 250 C and a pressure of 50 atmospheres is used along with a copper catalyst. Which one of the following changes in these conditions would increase the yield of methanol? A B C D increase in temperature decrease in temperature increase in mass of catalyst decrease in pressure 3 A mixture of potassium bromide and potassium sulphate contains 5 mol of potassium ions and 2 mol of bromide ions. How many moles of sulphate ions are present? A 1.5 B 2.0 C 2.5 D BP [Turn over

3 4 The following equilibrium is established when hydrogen fluoride is added to water at 25 C. HF(aq) H + (aq) + F (aq) If the concentrations of HF(aq) and F (aq) at equilibrium are mol dm 3 and mol dm 3 respectively, which one of the following is the value of the equilibrium constant? A mol dm 3 B mol dm 3 C mol dm 3 D mol dm 3 5 The equation for the reaction of alkali with bromobutane is: The rate equation for the reaction is The units of the rate constant are A mol. B mol 1. C s. D s 1. C 4 H 9 Br + KOH C 4 H 9 OH + KBr rate = k[c 4 H 9 Br] 6 In which one of the following reactions is the underlined compound acting as an acid? A NaH + H 2 O NaOH + H 2 B NH 3 + H 2 O NH+ 4 + OH C H 2 O + HCO 3 CO2 3 + H 3 O + D H 2 O + HPO2 4 H 2 PO 4 + OH BP

4 7 A substance gave an orange precipitate with 2,4-dinitrophenylhydrazine and it also reduced acidified potassium manganate(vii). To which class of compounds does it belong? A B C D alkene aldehyde ketone ester 8 The number of stereoisomers of a compound with the structure CH 3 CHBrCH CH 2 is geometric (cis-trans) optical A 0 0 B 0 2 C 2 0 D The variation in strength of an acid is related to oxidation number. Which one of the following acids is the weakest? A H 2 SO 4 B HClO 4 C HClO D HPO 3 10 A mixture of nitrogen and hydrogen, initially in the molar ratio 1:3, reached equilibrium with ammonia when 50% of the nitrogen had reacted. If the total pressure was P what is the partial pressure of ammonia in the equilibrium mixture? A P/8 B P/6 C P/4 D P/3 [Turn over

5 LiAlH 4 Section B Answer all five questions in the spaces provided. 11 Cinnamaldehyde is a yellow liquid which boils at 252 C and is obtained from cinnamon oil. In the oil it has a trans structure. H C C CHO H cinnamaldehyde (a) Suggest how you would obtain cinnamaldehyde from cinnamon oil. (b) Draw the structure of the cis form of cinnamaldehyde. [1] (c) Complete the following reactions of cinnamaldehyde by writing the structures of the organic products. HCN H C C CHO [O] H [3] 1 [Turn over

6 1 (d) Cinnamaldehyde can be identified by reaction with 2,4-dinitrophenylhydrazine, to form a hydrazone. (i) Write the equation for this reaction showing the full structure of the hydrazone. [3] (ii) Explain how you would prepare a sample of the purified hydrazone from cinnamaldehyde and use it to confirm the identify of the aldehyde. [4] Quality of written communication (e) Cinnamaldehyde undergoes an addition reaction with bromine. (i) Write an equation for the reaction. [1] (ii) Explain if the molecule produced contains any asymmetric centres. [1]

7 12 Sodium nitrite is used as a preservative in a variety of food products especially sausage meat. The amount present can be determined by titration with potassium permanganate. 2MnO 4 + 5NO 2 + 6H + 2Mn H 2 O + 5NO 3 (a) (i) Using oxidation numbers, explain why this reaction is a redox reaction. [3] (ii) In an experiment, all the sodium nitrite present in 1 kg of sausage meat was extracted using distilled water and the solution concentrated to 50 cm 3. The solution was placed in a burette and titrated against 25.0 cm 3 of acidified 0.02 M potassium manganate(vii) solution cm 3 of the solution was required to reach the end point. Calculate the percentage by mass of sodium nitrite present in the sausage meat. [4] (b) Sodium nitrite also acts as a reducing agent with bromine water which is decolourised forming an acidic solution of bromide and nitrate ions. Write an ionic equation for the reaction. [1] BP

8 (c) Sodium nitrite reacts with dilute mineral acids to form nitrous acid which is a weakly ionised, unstable acid known only in solution. (i) Write an equation for the formation of nitrous acid from sodium nitrite using dilute sulphuric acid. [1] (ii) The dissociation constant of nitrous acid is mol dm 3 at room temperature. Calculate the ph of a 0.1 M solution of nitrous acid. [3] (d) A mixture of sodium nitrite and nitrous acid could act as a buffer solution but in practice is of no use because of the instability of nitrous acid. (i) Explain the term buffer solution. (ii) Calculate the ph of a solution which is 0.1 mol dm 3 with respect to nitrous acid and 0.2 mol dm 3 with respect to sodium nitrite BP

9 13 The lattice enthalpy of caesium chloride can be determined using a Born Haber cycle. The table lists the data required. A Enthalpy change kj mol 1 lattice enthalpy of CsCl B atomisation of caesium +76 C atomisation of chlorine +122 D 1st ionisation energy of caesium +376 E 1st electron affinity of chlorine 349 F enthalpy of formation of CsCl 443 (a) (i) A Born Haber cycle is shown below. Put the letter for each enthalpy change in the appropriate box. (ii) Calculate the lattice enthalpy of caesium chloride. [Turn over

10 (b) Caesium chloride is the most soluble of all the Group I halides; g of the salt dissolves in 100 cm 3 of water at 25 C. (i) Calculate the molarity of this solution. [3] (ii) A solution of caesium chloride is neutral although ammonium chloride is acidic. Explain why the ph values of their solutions are different. (c) The relative atomic mass of caesium was originally determined by precipitating silver chloride from a solution of caesium chloride using silver nitrate solution. (i) Write an ionic equation for the reaction. [1] (ii) If g of silver chloride were obtained from g of caesium chloride, calculate the relative atomic mass of caesium. (Ag = and Cl = 35.45) [3].06BP

11 14 Oleic acid has the structure C 17 H 33 COOH and reacts with glycerol to form the oil triolein. (a) (i) Three molecules of oleic acid react with one molecule of glycerol to form triolein. Write the equation for the reaction. (ii) Triolein is a liquid at room temperature. Explain how it may be hardened. (b) The saponification value of an oil is the number of mg of potassium hydroxide needed to saponify 1 g of an oil. (i) Explain the term saponification. [1]

12 (ii) Calculate the saponification value of olive oil from the following data: 0.5 g of olive oil was placed in a round bottomed flask and 50 cm 3 of 0.1 M ethanolic potassium hydroxide added. The flask was fitted with a reflux condenser and the mixture boiled for about 45 minutes by which time the solution was clear. The solution was then titrated with 0.1 M hydrochloric acid to determine the unreacted potassium hydroxide. The titre value was 23.5 cm 3. [3] (c) Beeswax is not a triglyceride; it is a mixture of simple esters formed from straight chain acids and straight chain alcohols. One of the esters present in beeswax is C 25 H 51 CO 2 C 30 H 61. (i) Write the molecular formula for this ester. [1] (ii) Write the empirical formula for this ester. [1] (iii) Write the equation for the formation of this ester from the corresponding alcohol and acid. (iv) Write the equation for the hydrolysis of this ester using aqueous sodium hydroxide. (v) Beeswax has a melting point of C. Explain why the melting point is not sharp BP [1]

13 15 Phosphoric acid may be prepared in the laboratory by oxidising red phosphorus with concentrated nitric acid. P HNO 3 + H 2 O 4H 3 PO 4 + 5NO 2 + 5NO (a) Explain why the preparation should be carried out in a fume cupboard. [1] (b) The phosphoric acid formed is a syrupy liquid which dissolves easily in water. It reacts with alkalis to form salts. (i) Write an equation for the formation of sodium dihydrogen phosphate. [1] (ii) Write an equation for the formation of diammonium hydrogen phosphate, (NH 4 ) 2 HPO 4. [1] (iii) Calculate the percentage of nitrogen in diammonium hydrogen phosphate. (iv) Explain why diammonium hydrogen phosphate is used as a fertiliser. [Turn over

14 (c) Phosphoric acid is used to prepare hydrogen iodide from sodium iodide. Compare and contrast the reaction of sodium iodide with concentrated sulphuric and concentrated phosphoric acid [Turn over

15 ADVANCED General Certificate of Education 2006 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] WEDNESDAY 31 MAY, AFTERNOON MARK SCHEME

16 Section A 1 A 2 B 3 A 4 C 5 D 6 D 7 B 8 B 9 C 10 D for each correct answer [20] 20 Section A 20

17 Section B 11 (a) Fractional distillation (b) H C C H CHO [1] (c) H C C COOH H [1] H C C CH(OH)CN H [1] H C C CH 2 OH H [1] [3] (d) (i) Either the cis or trans structure is accepted H CHO C C + NH 2 NH NO 2 H NO 2 H C C CH H NNH NO 2 + H 2 O NO 2 [3] (ii) (Add 2,4-dinitrophenylhydrazine solution to cinnamaldehyde) filter off precipitate [1] recrystallise (from ethanol) [1] find melting point [1] comparison with known value [1] [4] Quality of written communication

18 (e) (i) H C C CHO H + Br 2 H Br C C H CHO Br [1] (ii) (Two centres with) carbon atom attached to four different groups [1] (a) (i) manganese +7 goes to +2 [1] nitrogen +3 goes to +5 [1] manganese reduced and nitrogen oxidised [1] [3] (ii) 25 cm 3 of 0.02 MnO 4 = 25 cm = mol 1 mol MnO 4 = 2.5 mol NO mol MnO 4 = mol NO 2 = mol mol NO 2 are contained in 10.5 cm 3 of solution // mol NO 2 are contained in 50 cm 3 of solution = mol NaNO 2 = = mol = = g % = 0.411/ = % [4] (b) Br 2 + H 2 O + NO 2 2Br + NO 3 + 2H + [1] (c) (i) 2NaNO 2 + H 2 SO 4 2HNO 2 + Na 2 SO 4 [1] (ii) K = = [H+ ] [NO 2 ] 0.1 = = [H + ] 2 [H + ] = ph = 2.17 [3] (d) (i) Constant ph [1] when small amounts of acid or alkali added [1] (ii) [H + ] = K [acid] [salt] = /0.2 = ph =

19 13 (a) (i) C E D B A F (ii) = LE = LE LE = +668 (b) (i) CsCl = = /168.5 = 1.10 mol Molarity = 11 M [3] (ii) Ammonium chloride formed from weak base and strong acid [1] Caesium chloride formed from strong base and strong acid [1] or Ammonium ion donates proton to water, Nl H 2 O ΝH 3 + H 3 O + [1] Caesium ion does not react with water [1] (c) (i) Ag + + Cl AgCl [1] (ii) AgCl = = g of silver chloride = 5.732/ = mol g CsCl = 0.04 mol 1 mol CsCl = 6.734/0.04 = Cs = = [3] (a) (i) CH 2 OH CH 2 OCOC 17 H 33 CHOH + 3C 17 H 33 COOH CHOCOC 17 H H 2 O CH 2 OH CH 2 OCOC 17 H 33 (ii) Finely divided nickel [1] Hydrogen [1] (b) (i) Alkaline hydrolysis [1] (ii) Volume of KOH reacted = cm 3 = 26.5 cm 3 moles of KOH = = mol KOH = = 56 grams of KOH = = g = 148 mg

20 0.5 g of oil required 148 mg of KOH 1 g of oil requires 296 mg saponification value = 296 [3] (c) (i) C 56 H 112 O 2 [1] (ii) C 28 H 56 O [1] (iii) C 25 H 51 COOH + C 30 H 61 OH C 25 H 51 CO 2 C 30 H 61 + H 2 O (iv) C 25 H 51 CO 2 C 30 H 61 + NaOH C 25 H 51 COONa + C 30 H 61 OH (v) Mixtures have a melting point range [1] (a) Nitrogen oxides are poisonous [1] (b) (i) H 3 PO 4 + NaOH NaH 2 PO 4 + H 2 O [1] (ii) 2NH 3 + H 3 PO 4 (NH 4 ) 2 HPO 4 [1] (iii) (NH 4 ) 2 HPO 4 = = 132 Percentage nitrogen = 28/ = 21.2% (iv) It contains nitrogen [1] and phosphorus [1] (c) HI formed from both acids [1] hydrogen sulphide, sulphur and iodine formed with H 2 SO 4 [1] or answers based on the reduction of sulphuric acid and the non-reduction of phosphoric acid H 2 SO 4 oxides HI/I I /HI reduces H 2 SO 4 I /HI reacts with H 2 SO 4 [1] H 2 SO 4 reacts with I /HI to form SO 2, H 2 S, S, I 2 (any 2) [1] 9 Total 90

21 ADVANCED General Certificate of Education January 2007 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] THURSDAY 11 JANUARY, MORNING TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all sixteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all six questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Quality of written communication will be assessed in question 15(c)(i). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

22 Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 Which one of the following alcohols does not undergo oxidation when treated with warm acidified potassium dichromate(vi)? A B C D 3-methylpentan-1-ol 3-methylpentan-2-ol 2-methylpentan-2-ol 2-methylpentan-1-ol 2 Toothpaste for sensitive teeth contains 10% by mass of hydrated strontium chloride, SrCl 2.6H 2 O. What is the mass of strontium contained in 100 g of toothpaste? A B C D 1.8 g 3.3 g 3.8 g 4.6 g 3 Which one of the following does not contain an asymmetric centre? A CH 3 CH(CH 3 )CH 2 CH 3 B CH 3 CH(OH)CH 2 CH 3 C CH 3 CHClCH 2 CH 3 D CH 3 CH(NH 2 )CH 2 CH 3

23 4 Chlorine reacts with water according to the equation below. Cl 2 + H 2 O HOCl + H + + Cl Which one of the following substances when added would move the equilibrium to the right? A B C D hydrogen hydrogen chloride sodium chloride sodium hydroxide 5 The concentration of hydrogen ions in a solution is mol dm 3. What is the concentration of hydroxide ions in the solution? A mol dm 3 B mol dm 3 C mol dm 3 D mol dm 3 6 The kinetics of the reaction of nitrogen(ii) oxide with hydrogen were investigated. The following data were obtained. 2NO + 2H 2 2H 2 O + N 2 [NO] mol dm [H 2 ] mol dm Relative rate of reaction What is the rate equation for the reaction? A rate = k[no][h 2 ] B rate = k[no] 2 [H 2 ] C rate = k[no] 2 [H 2 ] 2 D rate = k[no][h 2 ] 2

24 7 Which one of the following is used for the rate constant of a third order reaction? A s 1 B mol dm 3 s 1 C mol 2 dm 6 s 1 D mol 2 dm 6 s 1 8 For which one of the following titrations is there no suitable indicator? A B C D Na 2 CO 3 (aq) against H 2 SO 4 (aq) NH 3 (aq) against CH 3 COOH(aq) Ca(OH) 2 (aq) against HCl(aq) I 2 (aq) against Na 2 S 2 O 3 (aq) 9 The conjugate base of methanol is A OH B CH 3 O C CH 3 + D CH 3 O + 10 For which one of the following chlorides is it not possible to construct a Born-Haber cycle? A B C AgCl HCl RbCl D MgCl 2

25 Section B Answer all six questions in the spaces provided. 11 When chlorine gas is passed into aqueous sodium thiosulphate the products are sulphate(vi) ions, chloride ions, hydrogen ions and Na 2 S 2 O 3. (a) Write a balanced ionic equation for the reaction. (b) State the change in oxidation numbers for chlorine and sulphur in this reaction. (c) State the industrial use of the reaction between chlorine and sodium thiosulphate. [1]

26 12 The diagram shows how to distinguish between propanal and propanone. Tollen s reagent + propanal or propanone water heat (a) State the metal ion present in Tollen s reagent. [1] (b) State the functional group present in both propanal and propanone. [1] (c) Explain why hot water is used. [1] (d) State what is observed in separate experiments with propanal and propanone. Propanal [1] Propanone [1]

27 13 Poisonous carbon monoxide may be detected and estimated by several methods. (a) A sample of gas is believed to be pure carbon monoxide. How could you prove, using combustion, that the gas is carbon monoxide? (b) Carbon monoxide can be detected using a piece of filter paper soaked in palladium chloride. The paper blackens due to the formation of palladium by a redox reaction. CO + PdCl 2 + H 2 O CO 2 + 2HCl + Pd (i) Explain the meaning of the term redox. [1] (ii) Calculate the number of milligrams of palladium formed if 360 dm 3 of air containing 0.001% by volume of carbon monoxide are in contact with a piece of filter paper containing palladium chloride. Assume the reaction takes place at 20 C and a pressure of one atmosphere and the palladium chloride is in excess. [3]

28 (c) The traditional quantitative method of analysis is to pass air containing carbon monoxide over iodine pentoxide. Any carbon dioxide present in the air is removed beforehand. 5CO(g) + I 2 O 5 (s) 5CO 2 (g) + I 2 (s) The carbon dioxide formed is passed through baryta water (barium hydroxide solution) to form a precipitate of barium carbonate, BaCO 3, which is filtered, washed and weighed. (i) Draw a diagram of the labelled apparatus which could be used to pass air over iodine pentoxide and then immediately pass the air through baryta water. (ii) Write the equation for the reaction of barium hydroxide with carbon dioxide. [1] (iii) Calculate the percentage of carbon monoxide, by volume, in 30 dm 3 of air if g of barium carbonate are formed. [3]

29 (d) Electrochemical methods may be used to detect carbon monoxide. The reactions occurring in one detector are: At the positive electrode CO + H 2 O CO 2 + 2H + + 2e E = 0.10 V At the negative electrode O 2 + 4H + + 4e 2H 2 O E = V (i) Write the overall redox equation for the cell. [1] (ii) Calculate the emf of the cell formed. [1]

30 14 Fats are naturally occurring esters of long chain fatty acids and glycerol. The fatty acids may be saturated or unsaturated. (a) Fats may be produced by the equilibrium reaction between a fatty acid and glycerol. CH 2 OH CH 2 O.OCR CHOH + 3RCOOH CHO.OCR + 3H 2 O CH 2 OH CH 2 O.OCR (i) Name a catalyst that can be used in this reaction. [1] (ii) State the systematic name for glycerol. (iii) The fat may alternatively be produced by the reaction of an acyl chloride with glycerol. Write the equation for the reaction and explain why an equilibrium is not produced.

31 (b) The most important unsaturated fatty acids have 18 carbon atoms with one or more double bonds. Oleic acid contains one double bond and linolenic acid contains three. (i) Draw the structure of cis oleic acid. [1] (ii) In linolenic acid, CH 3 CH 2 CHCHCH 2 CHCHCH 2 CHCH(CH 2 ) 7 COOH, each double bond has a cis structure. Draw the structure of the acid. [1] (iii) Write the formula of stearic acid which is saturated and also contains 18 carbon atoms. [1]

32 (c) (i) A comparison between the degree of unsaturation of oils and fats can be made using bromine water. Samples of lard and olive oil can be dissolved in a solvent and treated with bromine water. Explain how you would carry this out naming an appropriate solvent and state the results expected. [3] Quality of written communication (ii) The degree of unsaturation of a fat or oil may be measured using the iodine value. Define the term iodine value. (iii) Triolein has a relative molecular mass of 884 and one molecule contains three double bonds. Using your definition calculate the iodine value of triolein. [3]

33 15 Chlorination of ethanoic acid produces three substituted chloroethanoic acids. The first step is: Cl 2 + CH 3 COOH CH 2 ClCOOH + HCl Data on the acids is shown below. Acid Boiling pka Dissociation LD 50 of point/ C constant/ sodium salt mol dm 3 Monochloroethanoic acid Dichloroethanoic acid Trichloroethanoic acid (a) (i) Suggest why all three acids have a greater boiling point than that of ethanoic acid which is 118 C. (ii) Calculate the pka of dichloroethanoic acid. [1] (b) Trichloroethanoic acid is almost as strong as mineral acids such as hydrochloric acid. Calculate the ph of a 0.1 mol dm 3 solution of trichloroethanoic acid. [3]

34 (c) The sodium salt of monochloroethanoic acid together with monochloroethanoic acid can act as a buffer solution. (i) Explain the term buffer. (ii) Use equations to explain how this buffer mixture is able to remove both H + and OH ions if an acid or alkali is added. (iii) Explain why a mixture of sulphuric acid and sodium sulphate cannot act as a buffer. [1] (d) The LD 50 is an indication of the poisonous nature of a compound. It is the number of milligrams per kg of body mass that will kill a person. Calculate the number of moles of sodium monochloroethanoate that will kill a man weighing 90 kg. [3]

35 16 Aluminium dissolves slowly in cold dilute hydrochloric acid but rapidly in hot concentrated hydrochloric acid. Dilute sulphuric acid has little effect but hot concentrated sulphuric acid dissolves the aluminium in a similar way to copper. (a) The aqueous solution of aluminium in hydrochloric acid deposits crystals of Al 2 Cl 6.12H 2 O. On heating, the hydrate decomposes, giving off fumes of hydrogen chloride and leaving aluminium oxide. (i) Write the equation for the decomposition of the hydrate. [1] (ii) Explain how you could confirm that hydrogen chloride was given off. (b) Aluminium chloride can also be obtained by passing dry chlorine over aluminium metal. (i) Write the equation for the formation of aluminium chloride. [1] (ii) Explain why the chlorine must be dry. [1] (iii) Aluminium chloride is believed to exist as a dimeric structure. Complete the diagram below; show the outer electrons and draw the two coordinate bonds, which hold the AlCl 3 molecules together. Cl Cl Cl Al Al Cl Cl Cl (iv) State one property, which shows that aluminium chloride is covalent rather than ionic. [3] [1]

36 (c) Aluminium sulphate is formed when either aluminium oxide or aluminium is dissolved in sulphuric acid. (i) Write the equation for the reaction of aluminium with hot, concentrated sulphuric acid. [1] (ii) Aluminium oxide also dissolves in alkalis. Write the equation for its reaction with sodium hydroxide and state the name given to an oxide, which dissolves in acids and alkalis. (iii) Explain why a solution of aluminium sulphate is acidic.

37 ADVANCED General Certificate of Education January 2007 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] ThurSDAy 11 JANuAry, MorNiNG MArk SChEME

38 Quality of Written Communication 2 marks The candidate expresses ideas clearly and fluently through well-linked sentences and paragraphs. Arguments are generally relevant and well-structured. There are few errors of grammar, punctuation and spelling. 1 mark The candidate expresses ideas clearly, if not always fluently. Arguments may sometimes stray from the point. There may be some errors of grammar, punctuation and spelling, but not such as to suggest a weakness in these areas. 0 marks The candidate expresses ideas satisfactorily, but without precision. Arguments may be of doubtful relevance or obscurely presented. Errors in grammar, punctuation and spelling are sufficiently intrusive to disrupt the understanding of the passage.

39 Section A 1 C 2 B A 4 D 5 C 6 B 7 D 8 B 9 B 10 B for each correct answer [20] 20 Section A 20

40 Section B 11 (a) S 2 O Cl 2 + 5H 2 O 2SO Cl + 10H + (b) Cl 0 1 [1] S [1] (c) Removal of chlorine/antichlor [1] 5 12 (a) Ag + /silver [1] (b) Carbonyl/C O [1] (c) Helps to speed up the reaction/slow at room temperature/flammable [1] (d) Propanal: silver mirror formed [1] Propanone: no change/solution remains colourless [1] 5 13 (a) (Burn the gas) to form carbon dioxide [1], add to limewater giving white precipitate/milky/chalky [1] (b) (i) Reduction and oxidation takes place (in the same reaction) [1] (ii) 360 dm 3 of air contains dm 3 carbon monoxide moles of carbon monoxide = 3.60/ = mol 1 mol of carbon monoxide gives 1 mol palladium mol palladium = = g = 15.9 mg [3] (c) (i) air and air CO iodine pentoxide baryta water

41 (ii) Ba(OH) 2 + CO 2 BaCO 3 + H 2 O [1] (iii) BaCO 3 = = g of BaCO 3 = 0.493/197 = mol 1 mol carbon monoxide = 1 mol carbon dioxide = 1 mol BaCO 3 mol CO = volume CO = dm 3 = 0.06 dm 3 % CO in air = 0.06/ = 0.2% [3] (d) (i) 2CO + O 2 2CO 2 [1] (ii) ( 0.10) = [1] (a) (i) Concentrated Sulphuric acid [1] (ii) Propane-1,2,3-triol (iii) CH 2 OH CH 2 OCOR CHOH + 3RCOCl CH 2 OCOR + 3HCl CH 2 OH CH 2 OCOR [1] Gas given off hence equilibrium not formed [1] (b) (i) (ii) [1] (iii) CH 3 (CH 2 ) 16 COOH/C 17 H 35 COOH/C 18 H 36 O 2 [1] (c) (i) Dissolve oil in e.g. trichloroethene [1] concept of fair test [1] lighter the colour the more unsaturated [1] [3] Quality of written communication (ii) Grams of iodine which saturates with 100g of oil (iii) 3 C C react with 3I 2 = 6I 884 g of triolein react with g = 762 g of iodine 1 g of triolein reacts with 0.86 g of iodine 100 g of triolein react with 86 g of iodine Iodine value = 86 [3] 18 [1]

42 15 (a) (i) Extra C Cl bonds create greater number of dipoles [1] stronger intermolecular forces [1] (ii) log ( ) = 1.29 [1] (b) K = [H+ ][X ] [HX] = [H + ] 2 = K[HX] = = [H + ] = 0.14 ph = 0.85 [3] (c) (i) Keeps ph constant [1] on addition of small amounts of acid or alkali [1] (ii) CH 2 ClCO 2 + H + CH 2 ClCO 2 H [1] CH 2 ClCOOH + OH CH 2 ClCO 2 + H 2 O [1] (iii) Sulphuric acid is a strong acid [1] (d) Lethal mass of sodium monochloroethanoate = = g ClCH 2 CO 2 Na = mol = /116.5 = [3] (a) (i) Al 2 Cl 6.12H 2 O Al 2 O 3 + 6HCl + 9H 2 O [1] (ii) Ammonia gas/concentrated ammonia solution [1] white fumes/smoke [1] (b) (i) 2Al + 3Cl 2 Al 2 Cl 6 [1] (ii) Aluminium chloride reacts with water [1] (iii) Cl Cl Cl Cl Cl Cl (iv) Reacts with water/sublimes/low melting point [1] [3]

43 (c) (i) 2Al + 3H 2 SO 4 Al 2 (SO 4 ) 3 + 3H 2 [1] or 2Al + 6H 2 SO 4 Al 2 (SO 4 ) 3 + 3SO 2 + 6H 2 O (ii) Al 2 O 3 + 2NaOH 2NaAlO 2 + H 2 O or Al 2 O 3 + 2NaOH + 3H 2 O 2NaAl(OH) 4 [1] amphoteric [1] (iii) Weak base + strong acid 14 explanation based on aluminium ion and sulphate ions Section B 70 Total 90

44 ADVANCED General Certificate of Education 2007 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] FRIDAY 25 MAY, MORNING TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all fifteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all five questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Quality of written communication will be assessed in Question 13(b)(i). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

45 Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 The reaction between propanone and hydrogen cyanide is described as A B C D electrophilic addition. electrophilic substitution. nucleophilic addition. nucleophilic substitution. 2 What is the ph of the buffer formed when 50 cm 3 of 0.20 M sodium hydroxide is added to 50 cm M ethanoic acid? (K a of ethanoic acid = mol dm 3 ) A 2.58 B 2.73 C 4.76 D Which one of the following sets of sugars will form a silver mirror with Tollen s reagent? A Fructose, glucose and maltose B Fructose, glucose and sucrose C Fructose, maltose and sucrose D Glucose, maltose and sucrose 4 Given the following standard electrode potentials: Zn 2+ (aq) + 2e Zn(s) 0.76 V Fe 2+ (aq) + 2e Fe(s) 0.44 V I 2 (aq) + 2e 2I (aq) V Fe 3+ (aq) + e Fe 2+ (aq) V Which one of the following statements is correct? A Zinc metal is the most powerful oxidising agent. B Iron metal will displace iodide ions from solution. C Iron(II) ions will reduce iodine to iodide ions. D Iodide ions will reduce iron(iii) ions to iron(ii) ions but not to iron.

46 5 Which one of the following represents the complex formed when thiosulphate ions are used as a fixer in photography? A B C D [Ag(S 2 O 3 ) 2 ] 3 (aq) [Ag 2 (S 2 O 3 ) 2 ] 2 (aq) [AgS 2 O 3 ] (aq) Ag 2 S 2 O 3 (s) 6 The table below shows the ph range over which some indicators change colour. Indicator ph range of colour change Salicyl yellow Thymol blue Bromothymol blue Malachite green Which one of the following indicators is suitable to establish the end point when adding 0.1 M HCl to 0.1 M NH 3? A B C D Bromothymol blue Malachite green Salicyl yellow Thymol blue 7 The partition coefficient of butanedioic acid between ethoxyethane and water is 5. What mass of butanedioic acid will be extracted when a solution containing 5.00 g of butanedioic acid in 100 cm 3 of water is shaken with 10 cm 3 of ethoxyethane? A B C D 0.50 g 1.67 g 3.33 g 4.50 g 8 Which one of the following salts dissolves in water to form an acidic solution? A B C D Ammonium chloride Lithium chloride Potassium hydrogencarbonate Sodium carbonate

47 9 Which one of the following compounds displays optical isomerism? A CH 3 CHOHCOOH B CH 2 OHCH 2 COOH C CH 2 OHCOOCH 3 D CH 2 OHCH 2 CHO 10 Which one of the following is a conjugate acid-base pair? Acid Conjugate base A H 2 SO 4 HSO 4 B HSO 4 H 3 O + C SO 4 2 HSO 4 D HSO 4 H 2 SO 4

48 Section B Answer all five questions in the spaces provided. 11 Dinitrogen pentoxide (N 2 O 5 ), when heated, decomposes according to the equation: 2N 2 O 5 (g) 2N 2 O 4 (g) + O 2 (g) (a) Giving no practical details, suggest one way by which the rate of this reaction could be measured. [1] (b) The following results were obtained for the reaction at 45 C. Rate of [N 2 O 5 ] 10 3 mol dm 3 disappearance of N 2 O mol dm 3 s (i) Plot a graph of these results and deduce the rate equation for the reaction rate of disappearance of N 2 O (mol dm 3 s 1 ) [N 2 O 5 ] 10 3 (mol dm 3 )

49 (ii) Calculate the value of the rate constant, stating its units.

50 12 The elements of the third period, sodium to chlorine, show a change from metallic to non-metallic character across the period. (a) Complete the table below giving the formula, classification (acidic, basic, amphoteric or neutral) and type of bonding present in each of the oxides of the elements listed. Element Formula of oxide Classification Type of bonding in oxide Aluminium Phosphorus Silicon [3] (b) Aluminium reacts with chlorine to form aluminium chloride, Al 2 Cl 6. (i) Showing the outer electrons only, draw a dot-cross diagram to show the bonding in aluminium chloride. [3] (ii) Write an equation for the reaction of aluminium chloride with water.

51 (c) Magnesium reacts slowly with cold water, but will burn in steam to form magnesium oxide. (i) Draw a labelled diagram of the apparatus you could use to burn magnesium in steam. (ii) The partially complete Born Haber Cycle for magnesium oxide is shown below. Mg 2+ (g) + O 2 (g) Mg 2+ (g) + O(g) + 2e Mg 2+ (g) + O 2 (g) + 2e 1 2 B Mg(g) O 2 (g) A Mg(s) O 2 (g) MgO(s) Name the changes A and B. A B

52 (iii) Using the data below, calculate the lattice enthalpy for magnesium oxide. kj mol 1 A +150 B Bond enthalpy for oxygen st & 2nd electron affinity for oxygen +650 Enthalpy of formation of magnesium oxide 602

53 13 Pheromones, used as a chemical communication system by insects, were first isolated and identified in (a) The isomers shown below are pheromones used by two different insects. CH 3 CH 2 CH 2 COCH 3 A (CH 3 ) 2 CHCH 2 CHO B (i) What is the systematic name for A? [1] (ii) Give a chemical test to distinguish between A and B, stating any observations you would make. [3] (iii) The cabbage white butterfly can detect as little as g of B. Calculate how many molecules of B are present in g. [3]

54 (b) The european paper wasp uses 3-methylbutanoic acid, (CH 3 ) 2 CHCH 2 COOH, as a pheromone. (i) Explain, giving experimental details, how a pure sample of 3-methylbutanoic acid could be prepared from the alcohol, 3-methylbutan-1-ol. [4] Quality of written communication (ii) The dissociation constant, K a, for 3-methylbutanoic acid is mol dm 3. Calculate the ph of a 0.1 M solution of 3-methylbutanoic acid. (iii) Give two observations when phosphorus(v) chloride is added to 3-methylbutanoic acid. (iv) Write an equation for the reaction in part (iii).

55 14 Iron Age man formed soap by boiling animal fat with water and wood ash, which is alkaline. (a) Fats are esters of propan-1,2,3-triol and fatty acids. (i) Draw the structure of the ester tristearin formed from stearic acid and propan-1,2,3-triol. (ii) Write an ionic equation for the reaction of tristearin with hydroxide ions. (b) The saponification value of a fat is a measure of the relative molecular masses of the fatty acids present. (i) Define the term saponification value. (ii) The following results were obtained when the saponification value for lard was determined. Mass of lard = 1.05 g Volume of 0.1 M KOH added = 50.0 cm 3 Volume of 0.1 M HCl needed to neutralise unreacted KOH = 13.3 cm 3 Calculate the saponification value for lard. [4]

56 (c) Olive oil is an unsaturated fat. The degree of unsaturation in a fat is measured using its iodine value. (i) Define the term iodine value. (ii) Olive oil may be hardened using nickel as a catalyst. Explain the chemistry of hardening. (d) Explain why nutritionists advise that our diet should be low in saturated fats. [1]

57 15 Sulphuric acid was first discovered in the 8th century by the alchemist Jabir ibn Hayyan. Today it is manufactured using the Contact Process. (a) One step in the manufacture is the formation of sulphur trioxide from sulphur dioxide. 2SO 2 (g) + O 2 (g) 2SO 3 (g) (i) State the conditions used for the above reaction. Catalyst: Pressure: Temperature: [3] (ii) Explain why these conditions are used. Catalyst: Pressure: Temperature: [3] (iii) Write an expression for K p for the equilibrium. [1]

58 (iv) In an experiment 2.00 moles of SO 2 and 2.00 moles of O 2 are mixed and allowed to reach equilibrium at 1100 K and Nm moles of SO 3 were present at equilibrium. Calculate the value of K p stating its units. [4] (b) Sulphuric acid is used in the manufacture of fertilisers such as superphosphate (Ca(H 2 PO 4 ) 2 ). (i) Write an equation for the formation of superphosphate. (ii) Calculate the percentage of phosphorus in superphosphate. (iii) State one advantage and one disadvantage of using artificial fertilisers such as superphosphate. Advantage: Disadvantage:

59 ADVANCED General Certificate of Education 2007 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] FRIDAY 25 MAY, MORNING MARK SCHEME

60 Section A 1 C 2 C 3 A 4 D 5 A 6 A 7 B 8 A 9 A 10 A for each correct answer [20] 20 Section A 20

61 Section B 11 (a) Change in volume/change in pressure with time [1] [1] (b) (i) Plotting and line of best fit [1] Rate = k[n 2 O 5 ] [1] (ii) k = Rate/[N 2 O 5 ] = e.g. ( )/( ) = [1] s 1 [1] 5 12 (a) Aluminium Al 2 O 3 amphoteric ionic Phosphorus P 2 O 5 / P 4 O 10 acidic covalent Silicon SiO 2 acidic covalent [1] [1] [1] (b) (i) [1] for each correct line [3] es between Al atoms [0] each error [ 1] i.e. not using both and not showing dative bonds/ or not showing all outer es on Cl atoms [3] (ii) Al 2 Cl 6 + 3H 2 O Al 2 O 3 + 6HCl (, [ 1] for each mistake) or Al 2 Cl 6 + 6H 2 O 2Al(OH) 3 + 6HCl (c) (i) rocksil soaked with water magnesium ribbon HEAT (, [ 1] for no labels) (ii) A (Heat of) atomisation of magnesium [1] B 1st and 2nd ionisation (energies) for magnesium [1] (iii) (596) +650 = H lat + ( 602) H lat = 3886 (kj mol 1 ) (, [ 1] for each mistake)

62 13 (a) (i) Pentan-2-one [1] (ii) B will turn H + /MnO 4 [1] from purple to colourless [1] or B will turn H + /Cr 2 O 2 [1] (from orange) to green [1] or B will turn Fehling s solution [1] (from blue) to red/brown (solid) [1] or B will give a silver mirror [1] with Tollen s Reagent [1] state no reaction with A 2,4-dinitrophenylhydrazine [1] compare mpts Also accept A will give a positive iodoform test [1] Yellow crystals [1] No reaction with B [1] [3] (iii) RFM of B = 86 Moles of B: ( )/86 = Number of molecules of B = each error [ 1] [3] (b) (i) Place a mixture of (sulphuric) acid and potassium dichromate (in a pear flask) or acidified permanganate (VII) [1] Add 3-methylbutan-1-ol slowly/anti bump [1] Heat the mixture under reflux [1] Distil off the 3-methylbutanoic acid [1] [4] Quality of written communication (ii) [H + ] 2 = Ka [Acid] = [H + ] = [1] ph = 1.91 [1] (iii) Bubbles/effervescence PCl 5 gets smaller/dissolves Vigorous reaction/heat evolved (Any two, [1] each) (iv) (CH 3 ) 2 CHCH 2 COOH + PCl 5 (CH 3 ) 2 CHCH 2 COCl + POCl 3 + HCl (, [ 1] for each mistake/unbalanced) (a) (i) O CH 2 O C C 17 H 35 O CH O C C 17 H 35 O CH 2 O C C 17 H 35 (, [ 1] for each mistake) (ii) C 3 H 5 (OOCC 17 H 35 ) 3 + 3OH CH 2 (OH)CH(OH)CH 2 OH + 3C 17 H 35 COO (, [ 1] for each mistake)

63 (b) (i) The number of milligrams of potassium hydroxide [1] needed to neutralise the fatty acids formed by the complete hydrolysis of 1 gram of fat [1] (ii) Moles of HCl used = [1] Moles of reacted KOH = ( ) ( ) = [1] Mass of KOH used = ( ) 56 = g = mg [1] Saponification value = 205.5/1.05 = [1] [4] (c) (i) The number of grams of iodine [1] which will react/saturate with 100 g of a fat (ii) Addition of hydrogen [1] across the double bonds [1] (d) Concept of the relationship between saturated fats and coronary heart disease/obesity [1] (a) (i) Catalyst: Vanadium(V) oxide/v 2 O 5 Temperature: 450 C Pressure: 1 10 atmospheres ([1] each) [3] (ii) The catalyst speeds up (both the forward and the reverse) reactions equally [1] A high pressure will favour a high yield of SO 3, as there are fewer molecules on the product side (move equation to RHS). However the conditions chosen give a high yield without needing the expense of a high pressure [1] (The reaction is exothermic,) therefore a high yield is favoured by a low temperature. (450 C is a compromise)/low temperature the reaction is too slow/the catalyst works best at this temperature [1] [3] (iii) K p = p(so 3 ) 2 p(so 2 ) 2 p(o 2 ) [1] (iv) Initial moles: SO 2 = 2.0; O 2 = 2.0; SO 3 = 0 Equilibrium moles: SO 2 = 0.2; O 2 = 1.1; SO 3 = 1.8 Mole fraction: SO 2 = ; O 2 = ; SO 3 = Partial pressure: SO 2 = ; O 2 = ; SO 3 = K p = ([3], [ 1] for each mistake, carry error through) Units = N 1 m 2 [1] [4]

64 (b) (i) Ca 3 (PO 4 ) 2 + 2H 2 SO 4 Ca(H 2 PO 4 ) 2 + 2CaSO 4 (, [ 1] for each mistake) (ii) 62/234 = 26.5% (, [ 1] for each mistake) (iii) Advantages: Increases crop yield Applies nutrients required (Any one or any suitable alternative [1]) Disadvantages: Expensive Pollution of water supply/eutrophication (Any one or any suitable alternative [1]) 17 Section B 70 Total 90

65 ADVANCED General Certificate of Education January 2008 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] THURSDAY 10 JANUARY, MORNING TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all fifteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter in the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all five questions in Section B. Write your answer in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Quality of written communication will be assessed in question 11(a). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

66 Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 Which one of the following is the correct formula for 4-chloro-2-methylpent-2-enoic acid? A B C D CH 3 CCl=CHCH(CH 3 )COOH (CH 3 ) 2 C=CHCHClCOOH CH 3 CH 2 CCl=C(CH 3 )COOH CH 3 CHClCH=C(CH 3 )COOH 2 The oxidation of ethanedioate (oxalate) ion by acidified manganate(vii) ions can be represented by the following equations. C 2 O 4 2 (aq) 2CO 2 (g) + 2e MnO 4 + 8H + + 5e Mn H 2 O What volume of 0.02 M potassium manganate(vii) is required to oxidise completely a solution containing 0.02 mole of ethanedioate ions? A 40 cm 3 B 100 cm 3 C 250 cm 3 D 400 cm 3 3 In which one of the following reactions does hydrogen behave as an oxidising agent? A H 2 + Cl 2 2HCl B N 2 + 3H 2 2NH 3 C C 2 H 4 + H 2 C 2 H 6 D 2Na + H 2 2NaH

67 4 Which one of the following oxides is amphoteric? A Al 2 O 3 B Cl 2 O 7 C P 4 O 10 D SiO 2 5 A mixture of 8.4 g of ethene and 5.6 g of but-1-ene in a closed vessel has a total pressure of 100 kpa. What is the partial pressure of ethene? A B C D 40 kpa 50 kpa 60 kpa 75 kpa 6 Given the half cell reactions: Mn 2+ (aq) + 2e Mn(s) 1.18 V Ag + (aq) + e Ag(s) V What is the e.m.f. of the cell? A B C D 0.38 V 1.98 V 2.78 V 3.16 V g of magnesium metal were added to an excess of a solution of an arsenic compound containing As n+ and 7.5 g of arsenic were deposited. What is the oxidation number of arsenic in the compound? A +2 B +3 C +4 D +5

68 8 Which one of the following pairs of structures are chiral isomers? H H A C C H Cl Cl Cl Cl H CH 3 H CH 3 H B C C C C CH 3 H H CH 3 OH OH C C C H COOH HOOC H CH 3 CH 3 H H D CH 3 CH 2 C CH 3 H 3 C C CH 2 CH 3 CH 3 CH 3 9 The rate of the reaction: 2H 2 (g) + 2NO(g) 2H 2 O(g) + N 2 (g) is first order with regard to H 2 and second order with respect to NO. What are the units for the rate constant? A mol 2 dm 6 s B mol 2 dm 6 s 1 C mol dm 3 s 1 D mol 1 dm 3 s

69 10 The diagram shows data for the neutralisation of 100 cm 3 of hydrochloric acid with sodium hydroxide solution of equal concentration. ph M 0.1 M 1M 1M 0.1 M 0.01 M Volume of sodium hydroxide added/cm 3 Which one of the following indicators would not be suitable for a titration of a given solution of hydrochloric acid (about 0.1 M) with sodium hydroxide solution of concentration 0.1 M? A congo red B chlorophenol red C litmus D neutral red

70 Section B Answer all five questions in the spaces provided. 11 The first step in the manufacture of nitric acid is the oxidation of ammonia. 4NH 3 + 5O 2 4NO + 6H 2 O The nitrogen(ii) oxide is converted into nitric acid in succeeding steps. (a) State the conditions used in the oxidation of ammonia and, using equations, explain how nitrogen(ii) oxide is converted to concentrated nitric acid. [5] Quality of written communication (b) Nitric acid reacts with copper to produce copper(ii) nitrate. The oxide of nitrogen formed depends on the concentration of the nitric acid. (i) Write the equation for the reaction of nitric acid with copper to produce nitrogen(iv) oxide. [1] (ii) Write the equation for the reaction of nitric acid with copper to produce nitrogen(ii) oxide.

71 (c) Industrially, nitric acid is used in the manufacture of ammonium nitrate and in forming adipic acid for the manufacture of nylon. (i) Write the equation for the formation of ammonium nitrate. [1] (ii) State and explain the use of ammonium nitrate. (iii) Write the equation for the formation of adipic acid from cyclohexanol using [O] to represent the oxidant.

72 12 Calcium hydride, CaH 2, is formed by the reaction of calcium with hydrogen at C. It was manufactured under the name of Hydrolith. When added to water a large volume of hydrogen is produced from a small mass of Hydrolith. This was used as a source of hydrogen in preference to transporting heavy steel cylinders. CaH 2 + 2H 2 O Ca(OH) 2 + 2H 2 (a) (i) Explain the reaction of calcium hydride with water in terms of the Brønsted Lowry theory of acids and bases. (ii) Calculate the volume of hydrogen given off at 20 C and one atmosphere pressure when 1.0 kg of calcium hydride is added to excess water. [3] (b) Calcium hydride can act as a reducing agent in a similar way to other metallic hydrides such as lithium aluminium hydride. Name two functional groups which are reduced by hydrides and state their reduction products.

73 (c) Calcium hydride is an ionic solid for which a Born Haber cycle can be constructed as shown below. Ca 2+ (g) + 2H(g) + 2e Ca 2+ (g) + H 2 (g) + 2e 436 kj mol 1 Ca 2+ (g) + 2H (g) 144 kj mol kj mol 1 Ca(g) + H 2 (g) 193 kj mol 1 Molar lattice enthalpy Ca(s) + H 2 (g) 189 kj mol 1 CaH 2 (s) (i) Write the electron structures of the calcium and hydride ions. [1] (ii) State the value of the H H bond enthalpy. [1] (iii) If the first ionisation enthalpy of calcium is 590 kj mol 1, calculate the second ionisation enthalpy. [1] (iv) Calculate the standard molar lattice enthalpy of calcium hydride.

74 13 Calcium hydroxyapatite, Ca 10 (PO 4 ) 6 (OH) 2, makes up 95% of tooth enamel and the remaining 5% contains proteins such as collagen. Tooth decay is caused when tooth enamel is attacked by acid in the mouth. Streptococcus mutans bacteria hydrolyse sucrose and eventually produce lactic acid. The critical ph in the mouth is between 5.2 and 5.5 when calcium ions are removed from the apatite. (a) Calculate the percentage of calcium in calcium hydroxyapatite. [3] (b) Streptococcus mutans bacteria hydrolyse sucrose. (i) Explain the term hydrolyse. [1] (ii) State another method of hydrolysing sucrose. (iii) Name the two sugars produced by the hydrolysis of sucrose.

75 (c) Lactic acid, CH 3 CHOHCOOH, has a pk a value of 3.86 at 25 C. Calculate the concentration of lactic acid in mg dm 3 present in saliva which would produce a ph of 5.2. Assume there is no buffering effect. [4] (d) Small changes in ph in the mouth are countered by buffer systems. Explain, using equations, how the carbonic acid/hydrogencarbonate ion buffer system works.

76 14 Biodiesel is a mixture of esters which can be made by heating a vegetable oil such as rapeseed oil with methanol in the presence of sodium hydroxide as a catalyst. The process is known as transesterification. C 21 H 39 COOCH 2 CH 2 OH C 21 H 39 COOCH + 3CH 3 OH 3C 21 H 39 COOCH 3 + CHOH C 21 H 39 COOCH 2 rapeseed oil The methyl ester is used as biodiesel. biodiesel CH 2 OH (a) Deduce the number of C=C double bonds in a molecule of the triglyceride in rapeseed oil. [1] (b) Suggest the meaning of the term transesterification. [1] (c) The diesel engine, as invented, was able to run on pure vegetable oil. However, modern diesel engines need a less viscous oil such as biodiesel. Suggest why biodiesel is less viscous than the triglyceride. (d) Vegetable oils like rapeseed oil are converted into solid fats for use in the food industry. Explain the chemistry involved in this hardening process. [3]

77 (e) One of the tests performed on oils is a titration to determine the acid value which is the number of milligrams of potassium hydroxide required to neutralise 1 g of the oil and indicates the amount of free acid present. (i) Calculate the acid value of 0.38 g of rapeseed oil dissolved in toluene (methylbenzene) and titrated against 0.1 M ethanolic potassium hydroxide solution. A titre of 24.5 cm 3 was needed. [3] (ii) Explain why it is necessary to shake the conical flask vigorously during the titration. [1] (f) A typical diesel molecule obtained from crude oil has the molecular formula C 16 H 34. (i) Write the equation for complete combustion of this hydrocarbon. (ii) Explain whether you would expect the complete combustion of biodiesel to produce the same products as the complete combustion of C 16 H 34. [1]

78 15 Phosgene, COCl 2, is a colourless gas which condenses readily to a liquid at 8 C. It has a pungent and suffocating smell and is highly poisonous. It was discovered in 1812 by the action of light on a mixture of carbon monoxide and chlorine which led to the name from the Greek phos (light) and gene (born). Cl O=C Cl Phosgene (a) It was originally thought that light catalysed the formation of phosgene. Explain why light is not a catalyst and suggest a more likely role of the light. (b) Phosgene is manufactured by passing carbon monoxide and chlorine through a bed of porous carbon which acts as a catalyst. CO(g) + Cl 2 (g) COCl 2 (g) Although the reaction is exothermic, it is carried out between 50 C and 150 C. (i) Explain the effect of increased pressure on the equilibrium. (ii) Explain the choice of the temperature range C. (iii) Suggest how phosgene can be removed from the equilibrium mixture. [1]

79 (c) A mixture of carbon monoxide and chlorine is allowed to reach gaseous equilibrium in a 10 dm 3 vessel. The initial mixture contained 2 mol of carbon monoxide and 5 mol of chlorine. At equilibrium, 1 mol of carbon monoxide remained. What is the equilibrium constant at the temperature of the experiment? [3] (d) Phosgene reacts in a similar way to acyl chlorides, RCOCl and thionyl chloride, SOCl 2. Write an equation for the reaction of phosgene with ethanol. (e) (i) Using outer electrons only, draw the electronic structure of phosgene. (ii) Explain the shape of a phosgene molecule, stating the approximate bond angles. [1]

80 ADVANCED General Certificate of Education 2008 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] THURSDAY 10 JANUARY, MORNING MARK SCHEME

81 Section A 1 D 2 D 3 D 4 A 5 D 6 B 7 B 8 C 9 B 10 A for each correct answer [20] 20 Section A 20

82 Section B 11 (a) 2NO + O 2 2NO 2 [1] 3NO 2 + H 2 O 2HNO 3 + NO [1] Platinum/rhodium catalyst [1] ~900 ºC [1] 7 8 atm [1] [5] Quality of written communication (b) (i) Cu + 4HNO 3 Cu(NO 3 ) 2 + 2H 2 O + 2NO 2 [1] (ii) 3Cu + 8HNO 3 3Cu(NO 3 ) 2 + 2NO + 4H 2 O (c) (i) NH 3 + HNO 3 NH 4 NO 3 [1] (ii) fertiliser [1] contains N [1] (iii) OH + 4 [O] HOOC(CH 2 ) 4 COOH + H 2 O (a) (i) hydride/h is the base [1] water/h 2 O is the acid [1] (ii) C 2 H 2 = 42 1 kg = = 23.8 mol dm 3 = /.9 dm 3 [3] (b) aldehyde 1 alcohol ketone 2 alcohol carboxylic acid 1 alcohol Any two (c) (i) Ca 2+, 1s 2 2s 2 2p 6 3s 2 3p 6 ; H, 1s 2 [1] (ii) 436 kj mol 1 [1] (iii) = 1150 kj mol 1 [1] (iv) = U U = = 2414 kj mol 1 12

83 13 (a) Ca 10 (PO 4 ) 6 (OH) 2 = = 1004 % Ca = = 39.8% [3] 1004 (b) (i) breaking bonds using water [1] (ii) acid [1] dilute heat Any one [1] (iii) glucose [1] fructose [1] (c) pk a = 3.86 K a = ph 5.2 [H + ] = K a = = [H+ ] 2 [HX] = ( ) 2 [HX] [HX] = C 3 H 6 O 3 = 90 [lactic acid] = = g J g in 1000 cm 3 = mg [4] (d) H 2 CO 3 H + + HCO 3 Can use either equilibrium equation HCO 3 + H + H 2 CO 3 or the two separate equations H 2 CO 3 + OH HCO 3 + H 2 O (a) C 21 H 39 saturated is C 21 H 43 4H 2C C 2 3 = 6 [1] [1] (b) exchange of ester groups [1] (c) the triglyceride is branched/not linear [1]/triglyceride has greater mass [1]/more van der Waals/greater forces of attraction [1]/more dipoles/ester groups [1]/greater forces of attraction get tangled [1] (d) hydrogen added to double bond [1] catalysed by nickel [1] greater attraction (between chains) [1] saturated single bonds/unsaturation removed [1] Any three [3] (e) (i) = mol KOH [1] 0.38 g of oil mol KOH 1 g of oil mol KOH KOH = = mol KOH = = g acid value = 361 [3]

84 (ii) oil and ethanolic solution do no easily mix [1] (f) (i) 2C 16 H O 2 32CO H 2 O (ii) yes contains C, H [1] (a) catalyst not used up light is/light is not a chemical [1] light provides energy to break bonds [1]/form free radicals (b) (i) 2 mol 1 mol [1] moves LHS RHS [1] (ii) high temperature low yield [1] low temperature high rate [1] (iii) cool mixture (below 8 C) [1] (c) start equilibrium K = CO Cl COCl [COCl 2 ] [CO] [Cl 2 ] = = mol 1 dm 3 [3] (d) COCl 2 + 2C 2 H 5 OH CO(OC 2 H 5 ) 2 + 2HCl COCl 2 + C 2 H 5 OH CO(OC 2 H 5 )Cl + HCl Any one COCl 2 + C 2 H 5 OH C 2 H 5 Cl + HCl + CO 2 (e) (i) x x x Cl x x x x x x x x O x x x x C x x x Cl x x x x (ii) O 120 C Cl Cl trigonal plan [1] 15 Section B 70 Total 90

85 ADVANCED General Certificate of Education 2008 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] THURSDAY 22 MAY, MORNING TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all fifteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all five questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Quality of written communication will be assessed in question 14(a)(iv). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

86 Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 The slowest stage in the production of sulphuric acid involves the conversion of sulphur dioxide to sulphur trioxide. 2SO 2 (g) + O 2 (g) 2SO 3 (g) ΔH = 197 kj What effect does adding a catalyst have on the rates of the forward and reverse reactions and the equilibrium constant? rate of forward reaction rate of reverse reaction equilibrium constant A decreases decreases increases B increases increases increases C increases decreases no effect D increases increases no effect 2 The partition coefficient of an organic compound X between ether and water is 20. An aqueous solution containing 5.00 g of X in 250 cm 3 of water was shaken with 100 cm 3 of ether. What mass of X remained in the aqueous layer following the extraction? A B C D 0.56 g 1.67 g 3.33 g 4.44 g 3 For the reaction H 2 SO 4 + HNO 3 HSO 4 + H 2 NO 3 + HNO 3 is the A conjugate acid of H 2 NO 3 + B conjugate acid of HSO 4 C conjugate base of H 2 NO 3 + D conjugate base of HSO 4 [Turn over

87 4 Which one of the following reactions in the Born Haber cycle for potassium iodide is exothermic? A KI(s) K + (g) + I (g) B K(g) K + (g) + e C I 2 (g) 2I(g) D I(g) + e I (g) 5 The pharmaceutical drug antifebrin, CH 3 CONHC 6 H 5, is made by the reaction of ethanoic anhydride with phenylamine. (CH 3 CO) 2 O + C 6 H 5 NH 2 CH 3 CONHC 6 H 5 + CH 3 COOH 6.0 g of ethanoic anhydride, (CH 3 CO) 2 O, reacted with 4.0 g of phenylamine, C 6 H 5 NH 2, to produce 3.8 g of antifebrin. The percentage yield is A 48.6% B 63.3% C 65.4% D 95.0% 6 In which one of the following reactions is no gas evolved? A B C D copper metal with concentrated nitric acid concentrated sulphuric acid with solid potassium iodide thionyl chloride with ethanoic acid aqueous sodium sulphite with potassium manganate(vii) solution

88 7 The mechanism for the reaction between propanone and iodine proceeds in a series of steps as follows: CH 3 COCH 3 + H 3 O + CH 3 C(OH) + CH 3 + H 2 O CH 3 C(OH) + CH 3 + H 2 O CH 2 = C(OH)CH 3 + H 3 O + CH 2 = C(OH)CH 3 + I 2 CH 2 ICOCH 3 + HI slow fast fast The orders with respect to propanone, hydroxonium (H 3 O + ) and iodine which support this would be: CH 3 COCH 3 H 3 O + I 2 A B C D Which one of the following equimolar salt solutions would have the highest ph? A B C D ammonium chloride ammonium ethanoate sodium chloride sodium ethanoate 9 Ammonia may be oxidised by mixing it with air and passing the mixture over a heated platinum rhodium catalyst. 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) Assuming air to be 20% oxygen, what volume of air is needed to react completely with 10.0 dm 3 of ammonia at 20 C and 1 atmosphere pressure? A 12.5 dm 3 B 40.0 dm 3 C 50.0 dm 3 D 62.5 dm 3

89 10 Given the following half-equations E / V Br 2 (aq) + 2e 2Br (aq) O 2 (g) + 4H + (aq) + 4e 2H 2 O(l) S 2 O 2 8 (aq) + 2e 2SO 2 4 (aq) which one of the following species could oxidise water to oxygen? A B C D Br (aq) Br 2 (aq) SO 2 4 (aq) S 2 O 2 8 (aq)

90 Section B Answer all five questions in the spaces provided. 11 Glucose is a white crystalline solid which exhibits the reactions of an aliphatic aldehyde. Its structure can be represented as: CHO CHOH CHOH CHOH CHOH CH 2 OH (a) State what is observed when glucose is boiled with Fehling s solution. [1] (b) Glucose is optically active. (i) Explain the meaning of the term optically active. [1] (ii) How many asymmetric centres are there in a glucose molecule? [1]

91 (c) Draw the structure of the product formed between glucose and 2,4-dinitrophenylhydrazine, representing glucose as RCHO. (d) Fermentation of glucose produces ethanol and carbon dioxide. The reaction is catalysed by the enzyme zymase found in yeast. (i) Write an equation for the fermentation of glucose. (ii) State what effect the enzyme has on the activation energy for this reaction. [1]

92 12 Nitrogen monoxide, NO, is a colourless gas which is formed in the reaction between moderately concentrated nitric acid and copper metal. In the presence of air it is immediately oxidised to the dioxide. (a) Write the equation for the formation of nitrogen monoxide from nitric acid and copper. (b) The oxidation of nitrogen monoxide is represented by the equation: 2NO(g) + O 2 (g) 2NO 2 (g) The kinetics of this reaction were studied and the following results recorded. Experiment Initial concentration of NO 10 3 mol dm 3 Initial concentration of O mol dm 3 Initial rate 10 4 mol dm 3 s (i) Using these results, deduce the order of the reaction with respect to nitrogen monoxide and oxygen and write the overall rate equation. order with respect to NO order with respect to O 2 rate equation [3] (ii) On the axes below, sketch the shape of the graph expected in each case. [NO] rate time [NO] [Turn over

93 (iii) Use the results for experiment 1 to determine the value of the rate constant and state its units. [3] (c) Nitrogen dioxide, NO 2, is a brown gas which dimerises to form colourless dinitrogen tetroxide, N 2 O 4. The following equilibrium is established. N 2 O 4 (g) 2NO 2 (g) ΔH = + 58 kj (i) State and explain the effect of reducing the total pressure on the above equilibrium. (ii) A sealed flask containing pure dinitrogen tetroxide was heated to 80 C and equilibrium allowed to establish. At equilibrium, the total pressure was 125 kpa and the mole fraction of dinitrogen tetroxide was found to be Calculate the value of K p for this reaction, stating its units. [4] (iii) State and explain the effect of increasing the temperature on the value of K p.

94 (d) Nitrogen dioxide dissolves in water to form an acidic solution. 2NO 2 + H 2 O HNO 3 + HNO 2 The nitrous acid decomposes to form more nitric acid. (i) Explain the relative strengths of nitrous and nitric acids. (ii) Given the half equations VO 2+ (aq) + 2H + (aq) +e V 3+ + H 2 O(l) E = V NO 3 (aq) + 4H + (aq) + 3e NO(g) + 2H 2 O(l) E = V VO 2 + (aq) + 2H + (aq) + e VO 2+ (aq) + H 2 O(l) E = V deduce the equation for the reaction which occurs when nitric acid is added to a solution containing a mixture of V 3+ and VO 2+ ions. (iii) A text book notes that nitrous acid can act as both an oxidising agent and a reducing agent. With reference to oxidation number, explain this statement by referring to the reactions of the acid with acidified aqueous solutions of iron(ii) sulphate and potassium manganate(vii). [4]

95 13 Using only elements from the third period of the Periodic Table, answer the following questions. (a) (i) Write the formula of the metallic chloride which contains both covalent and coordinate (dative) bonds. [1] (ii) Which element forms an oxide in which its oxidation state is +5? [1] (iii) Name the element which forms an oxide with a giant covalent structure. [1] (b) Aluminium oxide is amphoteric. (i) Explain the term amphoteric. [1] (ii) Write the equation for the reaction between aluminium oxide and sulphuric acid.

96 14 Linoleic acid (octadeca-9,12-dienoic acid), is one of two essential fatty acids in our diet since our bodies are unable to synthesise it. CH 3 (CH 2 ) 4 CH = CHCH 2 CH = CH(CH 2 ) 7 COOH linoleic acid Deficiency can lead to scaly skin and hair loss. Glyceryl esters of the acid are plentiful in sunflower oil. (a) (i) The configuration at each double bond is cis. Draw the structure of linoleic acid. [1] (ii) Draw the structure of the oil formed when one molecule of glycerol reacts with three molecules of linoleic acid, representing the acid as C 17 H 31 COOH. (iii) The iodine value for sunflower oil is typically in the range , while that of butter is Explain these differences.

97 (iv) Describe how the iodine value of a sample of sunflower oil may be determined. [4] Quality of written communication (b) Rancidity results from the oxidation of fats and oils in the absence of enzymes. This autoxidation may be slowed down by the addition of antioxidants such as citric acid which has the structure: CH 2 COOH HO C COOH CH 2 COOH (i) Write an equation to show the reaction of citric acid with excess sodium hydroxide solution. (ii) Titration of 25.0 cm 3 of a citric acid solution required 17.5 cm 3 of 0.1 M sodium hydroxide solution. Calculate the concentration of citric acid in g dm 3. [4]

98 15 Aldehydes and ketones are responsible for many familiar smells. Benzaldehyde is used to make almond essence while heptan-2-one gives blue cheese its odour. H C O CH 3 COCH 2 CH 2 CH 2 CH 2 CH 3 benzaldehyde C 6 H 5 CHO heptan-2-one (a) Fruits such as apricots contain amygdalin, C 20 H 27 O 11 N, which is hydrolysed by enzymes to form benzaldehyde, glucose and hydrogen cyanide. Write the equation for this reaction. (b) Benzaldehyde reacts with hydrogen cyanide to form benzaldehyde cyanohydrin. (i) Suggest the flow scheme for the mechanism of this reaction. (ii) Name the mechanism of this reaction. [3]

99 (c) Benzaldehyde may be oxidised using acidified potassium manganate(vii) to form benzoic acid, C 6 H 5 COOH. Benzoic acid is a weak acid with an acid dissociation constant, K a, of mol dm Calculate the ph of a M solution of benzoic acid. [3] (d) (i) Explain the relative solubilities of propanone and heptan-2-one in water. (ii) Name the organic product formed when heptan-2-one reacts with lithal, LiAlH 4. [1]

100 ADVANCED General Certificate of Education 2008 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] THURSDAY 22 MAY, MORNING MARK SCHEME

101 Section A 1 D 2 A 3 C 4 D 5 C 6 D 7 A 8 D 9 D 10 D for each correct answer [20] 20 Section A 20

102 Section B 11 (a) red precipitate [1] (b) (i) rotates plane of polarised light [1] (ii) 4 [1] (c) RCH = NNH O NO2 NO 2 (d) (i) C 6 H 12 O 6 2C 2 H 5 OH + 2CO 2 (ii) it lowers the activation energy [1] 8 12 (a) 3Cu + 8HNO 3 3Cu(NO 3 ) 2 + 2NO + 4H 2 O (b) (i) NO = 2 [1] O 2 = 1 [1] Rate = k[no] 2 [O 2 ] [1] [3] (ii) [NO] rate time [NO] (iii) Rate = k[no] 2 [O 2 ] = k ( ) 2 ( ) k = / k = dm 6 mol 2 s 1 [3] (c) (i) pushes equilibrium to right [1] (dependent on explanation) to increase number of molecules (and increase pressure) [1] (ii) mole fraction N 2 O 4 = 0.2 partial pressure N 2 O 4 = = 25 kpa mole fraction NO 2 = 0.8 partial pressure NO 2 = = 100 kpa K p = Ρ 2 NO2 /P N2 O 4 = /25 = /25 = 400 kρa [4]

103 (iii) K p explanation) to remove excess thermal energy/ drive towards endothermic change [1] (d) (i) nitric acid is stronger nitrogen is in +5 oxidation state in nitric acid [1] nitrogen is in +3 oxidation state in nitrous acid [1] nitrogen has a higher oxidation state in HNO 3 than in HNO 2 [1] Any two from three (ii) 3V 3+ + H 2 O + NO 3 3VO H + + NO (iii) acidified iron(ii) sulphate iron is oxidised [1] nitrogen is reduced [1] acidified potassium manganate(vii) manganese reduced [1] nitrogen oxidised [1] [4] (a) (i) Al 2 Cl 6 [1] (ii) phosphorus [1] (iii) silicon [1] (b) (i) reacts with acids and alkalis [1] (ii) Al 2 O 3 + 3H 2 SO 4 Al 2 (SO 4 ) 3 + 3H 2 O 6 14 (a) (i) H C C H H C C H CH 3 (CH 2 ) 4 CH 2 (CH 2 ) 7 COOH [1] (ii) CH 2 O COC 17 H 31 CH O COC 17 H 31 CH 2 O COC 17 H 31 (iii) sunflower oil [1] is more unsaturated/contains more C C double bonds [1] iodine value reflects degree of unsaturation [1]

104 (iv) known mass [1] add Wij s solution and place in dark, add KI [1] prepare a blank [1] titrate with standard thiosulphate solution using starch indicator (blue black to colourless) [1] [4] Quality of written communication (b) (i) CH 2 COOH CH 2 CO 2 Na HO C COOH + 3NaOH HO C CO 2 Na + 3H 2 O CH 2 COOH CH 2 CO 2 Na (ii) moles NaOH = /1000 = moles citric acid = /3 = = moles in 1 litre = = RMM citric acid = 192 concentration = = 4.48 (gdm 3 ) [4] (a) C 20 H 27 O 11 N + 2H 2 O C 6 H 5 CHO + 2C 6 H 12 O 6 + HCN (b) (i) H C O H O C CN H OH C CN O + CN O H + O [3] (ii) nucleophilic addition (c) K a = [H + ][C 6 H 5 COO ]/[C 6 H 5 COOH] = [H + ] 2 /[C 6 H 5 COOH] [H + ] 2 = [H + ] = moldm 3 ph = log[h+] ph = 3.6 [3] (d) (i) propanone is more soluble [1] (dependent on explanation) propanone has smaller (hydrophobic) hydrocarbon chain [1] (or vice versa for heptan-2-one) (ii) heptan-2-ol [1] 13 Section B 70 Total 90

105 ADVANCED General Certificate of Education January 2009 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] FRIDAY 9 JANUARY, AFTERNOON TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all fourteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all four questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Quality of written communication will be assessed in question 13(c). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

106 Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 The rate of decomposition of ethanal at 500 C is given by the equation below: rate = k [ethanal] 2 What are the units of k? A s 1 B mol dm 3 s 1 C mol 1 dm 3 s 1 D mol 2 dm 6 s 1 2 An organic compound, X, gives an orange crystalline product with 2,4-dinitrophenylhydrazine, but does not give a precipitate on heating with Fehling's solution. Which one of the following formulae is that of X? A HCHO B C 6 H 5 CH 2 CHO C CH 3 COCH 3 D CH 3 CH 2 CO 2 H 3 A gaseous mixture of 1.0 g of hydrogen and 2.8 g of nitrogen has a total pressure of kpa at a particular temperature. What is the partial pressure of hydrogen in the mixture? A B C D kpa kpa kpa kpa

107 4 Which one of the following oxides has a molecular structure as distinct from a giant structure? A Al 2 O 3 B Cl 2 O 7 C Na 2 O D SiO 2 5 How many moles of ethanoyl chloride would react with one mole of glucose, assuming that glucose can be represented by the formula CH 2 OH(CHOH) 4 CHO? A 1 B 4 C 5 D 6 6 Which one of the following alcohols, all with molecular formula C 5 H 12 O, could not be produced by the reduction of an aldehyde or a ketone? A B C D 2-methylbutan-1-ol 2-methylbutan-2-ol 3-methylbutan-1-ol 3-methylbutan-2-ol 7 An aqueous solution containing 1 mol of S 2 O 3 2 ions reduces 4 mol of Cl 2 molecules. Which one of the following is a product of the reaction? Note that water is a reactant. A S B SO 2 C SO 2 3 D SO 2 4

108 8 A 0.20 g sample of a monobasic acid requires 8.0 cm 3 of 0.40 mol dm 3 sodium hydroxide solution for complete reaction. Which one of the following is the relative molecular mass of the acid? A 62.5 B C D Pain is often felt when a piece of aluminium foil touches an amalgam filling in a tooth because an electrical current briefly flows. The amalgam contains tin. The standard electrode potentials are: Al e Al 1.66 V Sn e Sn 0.13 V Which one of the following statements concerning the resulting cell is correct? A Aluminium ions are produced from the foil. B The aluminium foil acts as the positive electrode. C The e.m.f. of the cell is V. D Tin ions are discharged into the saliva in the mouth. 10 An aqueous solution of ammonium chloride has a ph less then 7 because A B C D the ammonium ions donate protons to water molecules. the chloride ions combine with hydrogen ions to form hydrochloric acid. aqueous ammonium chloride is unstable and evolves ammonia gas leaving hydrochloric acid. the ammonium ions combine with hydroxide ions to form ammonium hydroxide leaving an excess of hydrogen ions.

109 Section B Answer all four questions in the spaces provided. 11 The extent of the manufacture of sulphuric acid was a major indicator of the wealth of a nation. Today the consumption of oil or ferrous metals shows the economic development of industrial nations. Sulphuric acid, however, remains a chemical that the developed world still needs. (a) Explain the use of sulphuric acid in the agricultural industry. (b) In the Contact process, sulphuric acid is manufactured from sulphur. Write three equations for the reactions occurring in this process. [3] (c) Sulphur dioxide is prevented from escaping to the atmosphere during the process. Explain the precautions taken against the emission of sulphur dioxide and why they are needed.

110 (d) Concentrated sulphuric acid reacts with copper metal. (i) Write an equation for the reaction [1] (ii) Using oxidation numbers, explain why the reaction can be regarded as a redox reaction. [3] (e) The strength of an acid is related to the value of the oxidation number of the central atom in the acid. Explain, using this theory, whether sulphuric acid is stronger than thiosulphurous acid, H 2 S 2 O 3. (f) A solution of sulphuric acid reacts with aqueous barium chloride. (i) Write an ionic equation for the reaction including state symbols. (ii) Describe what would be observed.

111 (iii) Calculate the mass, in milligrams, of barium sulphate produced if 19.0 cm 3 of 0.01 M sulphuric acid is added to 50 cm 3 of a barium chloride solution with a concentration of 0.16 g dm 3. [4]

112 12 The invention of the ph scale is credited to the Danish biochemist Sørenson whilst working for Carlsberg on problems connected with the brewing of lager. Control of acidity was essential. Continually referring to the hydrogen ion concentration was tedious and he suggested the use of a ph scale as a more convenient measure of acidity. (a) The acidity in lager is caused by weak acids. Explain the term weak acid. (b) When exposed to air, lagers and beers turn sour and the ph decreases. Suggest what causes this to happen. (c) A lager investigated by Sørenson had a hydrogen ion concentration of mol cm 3. Calculate the ph of this lager. (d) ph values depend on the temperature at which they are measured because of the variation of the ionic product of water with temperature, as shown in the table below. Temperature/K K w /mol 2 dm (i) Write an equation for the ionic product of water. [1] (ii) Deduce whether the dissociation of water is an exothermic or endothermic process. Explain your reasoning. [Turn over

113 (e) Lagers and beers are produced by the fermentation of sugars and starches. (i) Name a monosaccharide sugar. [1] (ii) Name the two types of polymer in starch. [1] (f) The carbon dioxide produced in the brewing process may be collected by dissolving in water under pressure. The carbonic acid and the hydrogencarbonate ion produced are involved in an equilibrium reaction which acts as a buffer system. (i) Using an equilibrium equation, explain the result of adding separately an acid and an alkali to this buffer system. (ii) Calculate how many grams of sodium ethanoate must be added to 500 cm 3 of 0.01 mol dm 3 ethanoic acid to produce a buffer solution of ph 5.8. K a (CH 3 COOH) = mol dm 3 [4]

114 13 The partially completed Born Haber cycle for magnesium chloride is shown below. Mg 2+ (g) + Cl 2 (g) + 2e Mg + (g) + Cl 2 (g) + e Mg(g) + Cl 2 (g) Mg(s) + Cl 2 (g) MgCl 2 (s) (a) (i) Complete the two empty boxes. (ii) Using the data below, calculate the lattice enthalpy for magnesium chloride. kj mol 1 First ionisation energy of magnesium +738 Second ionisation energy of magnesium Enthalpy of atomisation of magnesium +148 Enthalpy change of formation of magnesium chloride 641 Enthalpy of atomisation of chlorine +121 Electron affinity of chlorine 348 (iii) Explain, in terms of electrostatic forces and using magnesium chloride as an example, what is meant by the term lattice enthalpy. [Turn over

115 (iv) The lattice enthalpies of the magnesium halides calculated using the Born Haber cycle are shown below. Magnesium halide Magnesium fluoride Magnesium bromide Magnesium iodide Theoretical lattice enthalpy Suggest, using the enthalpy values in the Born Haber cycle, why the lattice enthalpies decrease. (b) Magnesium chloride has ionic bonding as described in the Born Haber cycle. Show the formation of magnesium chloride from magnesium and chlorine atoms using dot and cross diagrams. [3] (c) Magnesium iodide reacts with both sulphuric acid and phosphoric acid. Compare and contrast these reactions giving experimental observations and theoretical explanations. Equations are not required. [5] Quality of written communication

116 14 Natural fats and oils are generally a mixture of various esters of glycerol containing more than one kind of fatty acid, which may be saturated or unsaturated. A table of some oils and fats is shown below. Oil/fat Percentage of total fatty acids by mass saturated monounsaturated polyunsaturated Coconut oil Sunflower oil Lard Peanut oil (a) (i) Explain why it is important to have a mixture of saturated and unsaturated oils/fats in a balanced diet. (ii) Suggest the meaning of the term monounsaturated fatty acid. (iii) Name an unsaturated fatty acid found in some natural fats and oils. [1] (iv) Give the systematic name for glycerol, which reacts with fatty acids to form oils and fats.

117 (b) A sample containing 1.20 g of oil, containing a mixture of unsaturated triglycerides is saponified by mol potassium hydroxide. A second sample, also containing 1.20 g of the same oil, is found to react completely with mol hydrogen in the presence of a catalyst. (i) Calculate the number of moles of the triglycerides in the oil. [1] (ii) Calculate the average relative molecular mass of the triglycerides in the oil. [1] (iii) Calculate the average number of carbon carbon double bonds per fatty acid molecule in the original triglycerides. [1] (iv) Name the catalyst used in the hydrogenation. [1] (v) Suggest how you could show that the hydrogenated glyceride contains no carbon carbon double bonds. [3]

118 ADVANCED General Certificate of Education January 2009 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] FRIDAY 9 JANUARY, AFTERNOON MARK SCHEME Not to be circulated beyond the Examination Team

119 Section A 1 C 2 C 3 D 4 B 5 C 6 B 7 D 8 A 9 A 10 A for each correct answer [20] 20 Section A 20

120 Section B 11 (a) manufacture of superphosphate [1] which is used as a fertiliser/supply soluble phosphorus [1] (b) S + O 2 SO 2 [1] 2SO 2 + O 2 2SO 3 [1] SO 3 + H 2 O H 2 SO 4 [1] (c) sulphur dioxide absorbed in water/alkali/lime [1] to prevent acid rain [1] (d) (i) Cu + 2H 2 SO 4 CuSO 4 + SO 2 + 2H 2 O [1] (ii) before reaction: copper = 0 sulphur = +6 after reaction: copper = +2 sulphur = +4 copper is oxidised and sulphur is reduced [3] (e) the strongest acid has the highest oxidation number/sulphuric acid is the strongest acid thiosulphurous acid S = +2; sulphuric acid +6 (f) (i) Ba 2+ (aq) + SO 4 2 (aq) BaSO 4 (s) (ii) white [1] precipitate [1] from colourless [1] solutions (to max 2) (iii) mol of sulphuric acid = = mol 0.16 g of barium chloride dissolved in 1000 cm /20 g dissolved in 50 cm 3 = g one mol of barium chloride = = g = /208 = mol hence the sulphuric acid is in excess BaSO 4 = = 233 mass of barium sulphate = = g = 9 mg [4] (a) acid partially ionises/dissociates [1] producing (a low concentration of) hydrogen ions [1] (b) ethanol oxidised [1] ethanoic acid produced [1] (c) concentration = mol cm 3 = mol dm 3 ph = log ( ) = 4.3 (d) (i) K w = [H + ][OH ] [1] (ii) as the temperature goes up the value of K w increases hence the reaction goes to the RHS [1] the reaction must be endothermic [1]

121 (e) (i) e.g. glucose [1] (ii) amylose and amylopectin [1] (f) (i) H 2 CO 3 HCO 3 + H + addition of acid causes equilibrium to move to LHS/reacts with hydrogencarbonate ion [1] addition of alkali causes equilibrium to move to RHS/reacts with hydrogen ions [1] (ii) ph = pk a + log [CH 3 CO 2 Na]/[CH 3 CO 2 H] pk a = log ( ) = = log [CH 3 CO 2 Na]/[CH 3 CO 2 H] 1.07 = log[ch 3 CO 2 Na]/[CH 3 CO 2 H] = [CH 3 CO 2 Na]/[CH 3 CO 2 H] = [CH 3 CO 2 Na]/0.01 [CH 3 CO 2 Na] = mol dm 3 CH 3 CO 2 Na = = mol = = g g in 1 dm 3 hence 4.82 g in 500 cm 3 [4] (a) (i) Mg 2+ (g) + 2Cl(g) + 2e Mg 2+ (g) + 2Cl (g) (b) (ii) = U U = = (iii) lattice enthalpy is the energy/enthalpy needed to separate the Mg 2+ and Cl ions in a lattice to an infinite distance/long way (iv) the variables are bond energies and electron affinities the bond energies decrease and decrease U the electron affinities become less negative and increase U bond energy is more important Cl Mg Mg 2+ Cl Cl Cl [3]

122 (c) misty fumes (of HI) yellow solid (due to sulphur) black solid (due to solid iodine) smell of hydrogen sulphide gas smell of sulphur dioxide white solid at start violet/purple fumes (of iodine vapour) to a maximum of [3] the sulphuric acid oxidises HI/MgI 2 the phosphoric acid does not oxidise both acids react with MgI 2 to give HI to a maximum of [5] Quality of written communication (a) (i) saturated fats provide energy/insulation/protection unsaturated lower cholesterol building blocks for prostaglandins mixture means less saturated fats (ii) one [1] C=C double bond in the molecule [1] (iii) e.g. oleic acid [1] (iv) propane-1,2,3-triol (b) (i) 3 mol of KOH are needed to react with 1 mol of a triglyceride mol react with mol of the triglyceride number of moles = / [1] (ii) mol have a mass of 1.2 g 1 mol has a mass of 1.2/ = [1] = 1091 (iii) mol of hydrogen react with mol of the triglyceride 5.38/1.1 = 4.9 mol of hydrogen react with 1 mol of triglyceride each mol of the triglyceride contains 3 mol fatty acid hence each fatty acid contains 1.6 double bonds [1] (iv) nickel [1] (v) dissolve in a named non-aqueous solvent e.g. trichlorethane [1] add iodine/bromine solution (aqueous or suitable solvent) [1] if no double bonds no change in colour [1] 14 Section B 70 Total 90

123 ADVANCED General Certificate of Education 2009 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] THURSDAY 21 MAY, MORNING TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all sixteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter in the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all six questions in Section B. Write your answer in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Quality of written communication will be assessed in question 14(b). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

124 Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 Which one of the following substances, when added to water in equimolar amounts, will form a solution with the lowest ph? A B Na 2 O CH 3 COOH C SO 2 D SO 3 2 Which one of the following equations represents the lattice enthalpy of calcium bromide? A Ca(s) + Br 2 (l) CaBr 2 (s) B CaBr 2 (s) Ca(s) + Br 2 (g) C Ca 2+ (g) + 2Br (g) CaBr 2 (g) D CaBr 2 (s) Ca 2+ (g) + 2Br (g) 3 The rate constants for the forward and reverse reactions in the formation of nitrogen(iv) oxide are k 1 and k 2 respectively. 2NO + O 2 2NO 2 The equilibrium constant for the forward reaction is K. What is the effect of a catalyst on k 1, k 2 and K? k 1 k 2 K A decreases decreases decreases B increases increases increases C increases increases no effect D increases decreases no effect [Turn over

125 4 Concentrated nitric acid is used as A a dehydrating agent. B a hydrating agent. C an oxidising agent. D a reducing agent. 5 The rate equation for the reaction of iodide ions with hydrogen peroxide in acidic solution is What are the units of k? A mol 2 dm 6 s 1 B mol 1 dm 3 s 1 C mol dm 3 s 1 D mol 2 dm 6 s 1 rate = k[h 2 O 2 ] [H + ] [I ] 6 Heating sucrose with dilute hydrochloric acid produces A fructose only. B glucose only. C glucose and fructose. D glucose and maltose. 7 Which one of the following compounds produced a silver mirror when heated with Tollen s reagent? A CH 3 COCH 3 B CH 3 CO 2 H C CH 3 CHO D CH 3 CO 2 CH 3

126 8 Which one of the following molecules contains a chiral centre? A B C CH 3 CH = CHCl CH 3 CH 2 CH 2 CHO CH 3 CH(CH 3 )CO 2 H D CH 3 CH(OH)CO 2 CH 3 9 Which one of the following equations does not represent a redox reaction of nitric acid or the nitrate ion? A 8Al + 3NO H + 8Al NH H 2 O B 4H + + 2NO 3 + 2I 2H 2 O + 2NO 2 + I 2 C 2HNO 3 + K 2 CO 3 2KNO 3 + H 2 O + CO 2 D Pb + 4HNO 3 Pb(NO 3 ) 2 + 2H 2 O + 2NO 2 10 Given the following standard electrode potentials E /V Fe 2+ (aq) + 2e Fe(s) 0.44 Ni 2+ (aq) + 2e Ni(s) 0.25 Sn 2+ (aq) + 2e Sn(s) 0.14 Sn 4+ (aq) + 2e Sn 2+ (aq) I 2 (s) + 2e 2I (aq) Br 2 (l) + 2e 2Br (aq) which one of the following species is reduced by Sn 2+ (aq)? A B C D Br (l) Fe 2+ (aq) I 2 (s) Ni 2+ (aq)

127 Section B Answer all six questions in the spaces provided. 11 Some Scotch whiskies have the fragrance of cut grass. This smell is attributed to cis hex-3-enal, an unsaturated aldehyde. (a) Suggest a structure for cis hex-3-enal. (b) What would be observed if cis hex-3-enal is warmed with Fehling s solution? (c) Write the equation for the reaction between cis hex-3-enal and 2,4 dinitrophenylhydrazine. Represent the structure of cis hex-3-enal as C = O. There is no requirement to draw the full structure. [3]

128 12 The wing of a hang glider is made from sheets of polyethylene terephthalate (PET). The frame is an alloy of magnesium and aluminium. (a) (i) Draw the structures of the two monomers used to make PET. (ii) Draw the structure for one repeating unit of PET (b) Aluminium and magnesium have typical metal structures. (i) Draw a labelled diagram to show the bonding within a metal such as aluminium. (ii) State two properties of aluminium which make it suitable for use in the frame of a hang glider. (c) If the frame is burned, the aluminium and magnesium form a mixture of oxides. Write the equation for the reaction between aluminium and oxygen. [1] [Turn over

129 (d) Aluminium oxide is amphoteric, reacting with both acids and alkalis. (i) Write the equation for the reaction between aluminium oxide and sulphuric acid. (ii) Write the equation for the reaction between aluminium oxide and aqueous sodium hydroxide.

130 13 Car air bags contain a mixture of sodium azide, NaN 3, potassium nitrate, KNO 3, and silicon dioxide, SiO 2. In a collision, a series of chemical reactions produce nitrogen to fill the airbag. (a) Firstly, the sodium azide decomposes. (i) Write an equation for the decomposition of sodium azide to form sodium and nitrogen. [1] (ii) The azide ion can be written as + N = N = N Using a dot and cross diagram, draw the electron structure of the azide ion, showing the outer electrons of each atom. (b) Secondly, the potassium nitrate reacts with the sodium metal to form potassium oxide, sodium oxide and more nitrogen. (i) Write an equation for the reaction. [1] (ii) Use dot and cross diagrams to show the formation of sodium oxide from sodium and oxygen atoms [Turn over

131 (c) Metal oxides react with silicon dioxide to form metal silicates. Write an equation for the reaction of sodium oxide with silicon dioxide. [1] (d) The table below gives the percentage by mass of the ingredients in a typical air bag. Ingredient Percentage by mass sodium azide 65 silicon dioxide 25 potassium nitrate 10 Calculate the maximum volume of nitrogen which could be obtained from 100 g of this mixture at 20 C and a pressure of one atmosphere. [3] (e) Draw a diagram to explain the structure of silicon dioxide.

132 14 Rapeseed oil is a tri-ester of linoleic acid and has the structure shown below: CH 2 O C (CH 2 ) 7 CH = CH CH 2 CH = CH (CH 2 ) 4 CH 3 O O CH O C (CH 2 ) 7 CH = CH CH 2 CH = CH (CH 2 ) 4 CH 3 O CH 2 O C (CH 2 ) 7 CH = CH CH 2 CH = CH (CH 2 ) 4 CH 3 (a) Rapeseed oil can be converted into biodiesel. The tri-ester is hydrolysed to form glycerol and linoleic acid. Esterification of the linoleic acid with methanol produces biodiesel. (i) Draw the structure of glycerol. [1] (ii) Draw the structure of a biodiesel molecule.

133 (b) Describe how Wij s solution is used to determine the iodine value of rapeseed oil. No reference need be made to calculating the iodine value and no equations are required. [5] Quality of written communication (c) Linoleic acid reacts with thionyl chloride to produce an acyl chloride. Write an equation for the reaction. (d) Calculate the volume of hydrogen needed to saturate the double bonds in 100 g of linoleic acid (RMM = 280). [3]

134 15 Phosphorus pentachloride when pure is an almost colourless solid. X-ray analysis shows that it is composed of [PCl 4 ] + and [PCl 6 ] ions. Cl Cl + Cl Cl Cl P Cl Cl Cl P Cl Cl Cl Cl P Cl Cl Cl PCl 5 PCl 4 + PCl 6 (a) (i) State the shapes of the [PCl 4 ] + and [PCl 6 ] ions. [PCl 4 ] + [1] [PCl 6 ] [1] (ii) Calculate the oxidation number of phosphorus in [PCl 4 ] + and [PCl 6 ]. [1] (b) Phosphorus pentachloride reacts with carboxylic acids. Write the equation for the reaction between phosphorus pentachloride and ethanoic acid.

135 (c) When heated, phosphorus pentachloride vapourises and decomposes to form an equilibrium mixture. PCl 5 (g) PCl 3 (g) + Cl 2 (g) ΔH = +91 kj (i) Explain the effect of increasing the pressure on the equilibrium system. (ii) Explain the effect of increasing the temperature on the equilibrium system. (iii) If the equilibrium mixture contains 0.11 mol of phosphorus trichloride, 0.11 mol of chlorine and 0.39 mol of phosphorus pentachloride in a 1 dm 3 container at 300 C and Pa, calculate the dissociation constant, K p and state its units. [3]

136 16 Bromothymol blue is an indicator which changes colour over a ph range of At ph 6.0 it is yellow, above ph 7.8 it is blue. (a) Bromothymol blue can be regarded as a weak acid HIn which is in equilibrium with the In ion. HIn H + + In (i) State the conjugate base and conjugate acid in the equilibrium. conjugate base [1] conjugate acid [1] (ii) Using the equilibrium equation, explain the colour changes that occur when acid and alkali are added separately to the indicator. (b) The titration curve below shows the titration of 0.1M ethanoic acid with sodium hydroxide. 12 ph volume of 0.1M NaOH/cm 3 40 (i) Calculate the ph of the ethanoic acid solution at the start of the titration. (K a for ethanoic acid = mol dm 3 )

137 (ii) Explain whether bromothymol blue would be a suitable indicator for the titration. (iii) Write an equation for the reaction of ethanoic acid with sodium hydroxide. [1] (iv) Explain why a solution of sodium ethanoate is alkaline.

138 ADVANCED General Certificate of Education 2009 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] THURSDAY 21 MAY, MORNING MARK SCHEME

139 Section A 1 D 2 D 3 C 4 C 5 A 6 C 7 C 8 D 9 C 10 C for each correct answer [20] 20 Section A 20

140 Section B 11 (a) H H C = C CH 3 CH 2 CH 2 CHO (b) red (brown) [1] precipitate [1] (c) C = O + NH 2 NH C = NNH NO 2 NO 2 + H 2 O NO 2 NO 2 [3] 7 12 (a) (i) HOCH 2 CH 2 OH [1] (ii) HOOC COOH O O CH 2 CH 2 O C C O [1] (b) (i) electrons cation (ii) low density* [1] strong/ductile/rigid [1] (c) 4Al + 3O 2 2Al 2 O 3 [1] (d) (i) Al 2 O 3 + 3H 2 SO 4 Al 2 (SO 4 ) 3 + 3H 2 O (ii) Al 2 O 3 + 2NaOH + 3H 2 O 2NaAl(OH) 4 13 or Al 2 O 3 + 2NaOH 2NaAlO 2 + H 2 O

141 13 (a) (i) 2NaN 3 2Na + 3N 2 [1] (ii) N N N (b) (i) 2KNO Na 5Na 2 O + K 2 O + N 2 [1] (ii) Na O Na+ O 2 Na Na + (c) Na 2 O + SiO 2 Na 2 SiO 3 [1] (d) NaN 3 = = g = 1.0 mol KNO 3 = = g = 0.1 mol 1.0 mol NaN 1.5 mol N mol KNO mol N 2 Total number of mol N 2 = 1.55 mol Volume of N 2 = dm 3 = 37.2 dm 3 [3] (e) O O Si O O O Si O O 12 5

142 14 (a) (i) CH 2 OH CHOH CH 2 OH [1] (ii) CH 3 OCO(CH 2 ) 7 CH = CHCH 2 CH = CH(CH 2 ) 4 CH 3 (b) mass of fat [1] dissolved in named (chlorinated) solvent [1] mixed with Wij s solution [1] left in dark (for about 30 min) KI added [1] titrated against standard sodium thiosulphate solution) starch indicator blue\black to colourless [1] blank titration [1] to a maximum of [5] [5] Quality of written communication (c) CH 3 (CH 2 ) 4 CH = CHCH 2 CH = CH(CH 2 ) 7 COOH + SOCl 2 CH 3 (CH 2 ) 4 CH = CHCH 2 CH = CH(CH 2 ) 7 COCl + SO 2 + HCl or C 17 H 31 COOH + SOCl 2 C 17 H 31 COCl + SO 2 + HCl (d) 100 g = 100/280 mol = 0.36 mol of linoleic acid there are 2 double bonds in 1 molecule of linoleic acid hence mol = 0.72 mol hydrogen = dm 3 = dm 3 [3] 15 [Turn over

143 15 (a) (i) PCl 4 + tetrahedral [1] PCl 6 octahedral [1] (ii) PCl PCl 6 +5 [1] (b) PCl 5 + CH 3 COOH CH 3 COCl + HCl + POCl 3 (c) (i) equilibrium moves to LHS to reduce pressure essential [1] more moles on RHS [1] (ii) equilibrium moves to RHS to absorb heat essential [1] the reaction is endothermic [1] (iii) total number of moles = = 0.61 partial pressure of PCl 3 and Cl 2 = 0.11/ Pa = Pa partial pressure of PCl 5 = 0.39/ Pa = Pa P PCl3 P Cl K p = = P PCl = Pa [3] (a) (i) base = In [1] acid = HIn [1] (ii) OH reacts with H + equilibrium moves to RHS blue [1] Adding acid moves equilibrium to the LHS yellow [1] [H + ] [CH 3 CO 2 ] (b) (i) K a = = [CH 3 CO 2 ] = [H + ] 2 /0.1 [H + ] = ph = 2.89 (ii) yes, the vertical region of the titration curve is [1] within the region [1] (iii) NaOH + CH 3 COOH CH 3 CO 2 Na + H 2 O [1] (iv) weak acid and strong base (form the salt) [1] CH 3 COO + H 2 O CH 3 COOH + OH (1) [1] 11 Section B 70 Total 90 7

144 ADVANCED General Certificate of Education January 2010 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] THURSDAY 21 JANUARY, AFTERNOON TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all fifteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter in the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all five questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Quality of written communication will be assessed in question 11(a). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

145 Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 Which one of the following always has units? A B C D K a K c ph pk a 2 A compound gave a precipitate with 2,4-dinitrophenylhydrazine, but did not reduce acidified potassium dichromate. To which class of compounds does it belong? A B C D alkenes aldehydes ketones esters 3 Which one of the following oxides dissolves in water to form an alkaline solution? A B C D sodium oxide phosphorus pentoxide silicon dioxide sulphur trioxide 4 Which one of the following compounds reacts with propanoic acid to form propanoyl chloride? A B C D chlorine chloropropane hydrogen chloride thionyl chloride [Turn over

146 5 Which one of the following molecules exhibits optical isomerism? A CH 3 CH CHCH 3 B CH 3 CH 2 COCH 3 C CH 3 CH 2 CHClCH 3 D CH 3 CH 2 CH(CH 3 )CH 3 6 How many isomers are there of C 4 H 10? A 1 B 2 C 3 D 4 7 Overall, the rate of reaction between X and Y is third order. Which one of the following equations is not correct? A Rate = k[x] 0 [Y] 3 B Rate = k[x] 1 [Y] 2 C Rate = k[x] 1 [Y] 3 D Rate = k[x] 2 [Y] 1 8 Which one of the following carbohydrates is a polysaccharide? A B C D amylose fructose glucose maltose 9 Which one of the following represents the units for a rate constant of a third order reaction? A s 1 B mol dm 3 s 1 C mol 2 dm 6 s 1 D mol 2 dm 6 s 1

147 10 Which one of the following observations about the reaction between sodium iodide and concentrated sulphuric acid is correct? A A red solid is formed B A light brown gas is formed C A strong smelling gas is produced D A colourless solution remains [Turn over

148 Section B Answer all five questions in the spaces provided. 11 The manufacture of sulphuric acid remains as important today as when Liebig (the inventor of the condenser) wrote in 1843, We may fairly judge the commercial prosperity of a country from the amount of sulphuric acid it consumes. (a) Using equations, describe the manufacture of concentrated sulphuric acid from sulphur, explaining the conditions used. [5] Quality of written communication (b) State the problem caused by possible sulphur dioxide emissions during the manufacture of sulphuric acid. [1] (c) Explain one major use of sulphuric acid.

149 12 Hydrogen cyanide, HCN, is a colourless liquid with a boiling point of 26 C. It is a highly toxic substance; 50 mg of hydrogen cyanide will cause death within a few seconds. (a) Calculate the lethal dose (50 mg) of hydrogen cyanide in moles. [3] (b) Draw a dot and cross diagram of the structure of hydrogen cyanide, showing the outer electrons only. (c) Hydrogen cyanide is manufactured by passing a mixture of ammonia and methane over a platinum catalyst. The reaction is endothermic. NH 3 (g) + CH 4 (g) HCN(g) + 3H 2 (g) (i) Suggest why the reaction is carried out at 1000 C. (ii) Explain if a high pressure should be used in the manufacture of hydrogen cyanide. [Turn over

150 (iii) If ammonia (0.2 mol) and methane (0.2 mol) are placed in a 1dm 3 container and heated to 500 C, it is found that 0.1 mol of hydrogen cyanide and 0.3 mol of hydrogen are produced at one atmosphere pressure. Calculate the equilibrium constant, K c, for the reaction under these conditions and state its units. [3] (d) Hydrogen cyanide dissolves in water to form a weakly acidic solution. It has a dissociation constant of at 25 C. Alkalis react with hydrogen cyanide to form salts known as cyanides. (i) Write an equation for the formation of sodium cyanide from hydrogen cyanide. [1] (ii) Explain why an aqueous solution of sodium cyanide is alkaline. (iii) Using equations, explain how a mixture of sodium cyanide and hydrogen cyanide is able to act as a buffer.

151 (iv) Calculate the ph of the buffer solution formed when 200 cm 3 of a 0.5 mol dm 3 solution of hydrogen cyanide is added to 200 cm 3 of a 1.0 mol dm 3 solution of sodium cyanide. [3] (e) Hydrogen cyanide reacts with propanone to form an addition product known as a cyanohydrin. The reaction is catalysed by sodium hydroxide. (i) Write the equation for the reaction between hydrogen cyanide and propanone. (ii) Draw a flow scheme to illustrate the mechanism for the reaction. [3]

152 13 The partially completed Born Haber cycle for rubidium chloride is shown below. Rb + (g) + Cl(g) + e Rb + (g) + Cl (g) Rb(s) Cl 2 (g) (a) (i) Complete the empty boxes. (ii) Using the data below, calculate the enthalpy of formation for rubidium chloride. kj mol 1 First ionisation energy of rubidium +403 Enthalpy of atomisation of rubidium +81 Bond enthalpy of chlorine (Cl 2 ) +242 Electron affinity of chlorine 348 Lattice enthalpy of rubidium chloride +685 [Turn over

153 (b) The lattice enthalpies for Group I chlorides are listed below. Chloride Lattice enthalpy, kj mol 1 lithium chloride 848 sodium chloride 780 potassium chloride 711 rubidium chloride 685 caesium chloride 661 Suggest why the lattice enthalpy decreases as you descend the group. [1] (c) The flame colour of rubidium is red, which led it to be named after the Latin word rubidos, which means red. (i) Name another element which gives a red flame colour. [1] (ii) Describe how you would carry out a flame test using rubidium oxide. [3]

154 14 Vegetable oils are triglycerides formed by the esterification of glycerol with long chain organic acids such as oleic and stearic acids. (a) Draw the structure of glycerol. [1] (b) Explain the term esterification. (c) The iodine value is a measure of the degree of unsaturation of an oil. (i) Define the term iodine value. (ii) The iodine value of a vegetable oil was determined using the following procedure: 0.9 g of oil was added to 11.0 cm 3 of Wij s solution. The mixture was left to stand in the dark for 30 minutes. Then 20 cm 3 of 10% potassium iodide solution were added and the iodine formed reacted with 6.0 cm 3 of 0.1 M sodium thiosulphate solution. The blank titration required 46.0 cm 3 of the sodium thiosulphate solution. Calculate the iodine value of the vegetable oil. [3]

155 (iii) Explain why fats and oils formed from a mixture of stearic and oleic acids have lower iodine values than those formed from oleic acid only. [1] (d) Vegetable oils can be burnt and yield products similar to those formed by the combustion of hydrocarbons. (i) Name the products of the complete combustion of alkanes or vegetable oils. (ii) Name one product formed by their incomplete combustion. [1] (iii) Explain the environmental problems associated with the combustion of organic materials.

156 15 The titration curve for the reaction of 0.1 M sulphuric acid with 0.2 M ammonia solution is shown below. 12 ph volume of ammonia solution added/cm 3 (a) (i) Write the equation for the reaction of sulphuric acid with ammonia. (ii) Explain why ammonia is regarded as a Lowry Brønsted base in this reaction. [1] (b) (i) Name a suitable indicator for the titration. [1] (ii) Using the titration curve, explain why this indicator is suitable. [1] [Turn over

157 (c) Estimate the ph reached by the titration curve when a very large excess of ammonia solution has been added. K b ammonia = for NH 3 (aq) + H 2 O(l) OH (aq) + NH + 4 (aq) [4] (d) Ammonia reacts with ethanoic acid to form ammonium ethanoate. (i) Write an equation for the reaction. [1] (ii) Explain why it is not feasible to measure an accurate end point in the titration of ammonia with ethanoic acid.

158 ADVANCED General Certificate of Education January 2010 Chemistry Assessment Unit A2 1 assessing Module 4: Further Organic, Physical and Inorganic Chemistry [A2C11] THURSDAY 21 JANUARY, AFTERNOON MARK SCHEME

159 Section A 1 A 2 C 3 A 4 D 5 C 6 B 7 C 8 A 9 D 10 C for each correct answer [20] 20 Section A 20

160 11 (a) S + O 2 SO 2 (1) 2SO 2 + O 2 2SO 3 (1) H 2 SO 3 + H 2 O H 2 SO 4 } H 2 SO 2 + SO 3 H 2 S 2 O 7 Any (1) H 2 S 2 O 7 + H 2 O 2H 2 SO 4 Max [3] pressure: 1 10atm catalyst: V 2 0 5, vanadium pentoxide temperature: ºC/450ºC explanation of dissolving SO 3 Max [3] To Max of [5] QWC (b) Acid rain/equivalent description [1] (c) e.g. Use in manufacture of superphosphate [1] To dissolve phosphorus/make fertilisers [1] (a) 50mg = g = g (b) HCN = = 27 moles = /27 =.05/27 = mol [3] H C N (c) (i) (reaction endothermic) high temp RHS [1] speeds reaction up [1] (ii) more molecules (etc) on RHS [1] should not be used (conditional on first statement) [1] (iii) NH 3 + CH 4 HCN + 3H K c = = = Units = [ ] 4 / [ ] 2 = [ ] 2 = mol 2 dm 6 [3]

161 (d) (i) NaOH + HCN NaCN + H 2 O [1] (ii) NaOH is a strong base HCN is a weak acid or explanation based on CN ion (iii) CN + H + HCN + explanation [1] HCN + OH H 2 O + CN + explanation [1] 200 (iv) [HCN] : mol HCN = 0.5 = volume = = 400cm mol in 400cm 3 [ 0.25 mol dm 3 } [CN 200 ] : mol NaCN = 1.0 = volume = = 400cm mol in 400cm 3 [ 0.50 mol dm 3 k = [H + ] 0.5 = = 2 [H + ] 0.25 [H + ] = ph = 9.61 (e) (i) CH 3 CH 3 C = O + HCN CH 3 CH 3 C OH CN (ii) CH 3 CH 3 CH 3 O CH 3 C = O C H+ /HCN C CN CH 3 CN CH 3 OH CN [3] 25

162 13 (a) (i) Rb + 1 (g) + Cl 2 (g) + e 2 on Rb(g) + Cl(g) 1 Rb(g) + Cl 2 (g) 2 on Rb(g) + Cl(g) (ii) /2 348 = nh = nh nh = 428 (KJ mol 1 ) (b) ionisation energy of alkali metal decreases/cation size increases down group [1] (c) (i) lithium/calcium/strontium [1] (ii) add to concentrated HCl [1] Pt/nichrome wire/silica rod [1] blue flame bunsen [1] 9 14 (a) CH 2 OH CHOH CH 2 OH [1] (b) reaction of an alcohol with an acid to form an ester (c) (i) mass of iodine in grams which reacts with 100g of oil/fat (ii) cm 3 thoisulphate sol used = mol thoisulphate = mol 2Na 2 S 2 O 3 + I 2 2NaI + Na 2 S 4 O 6 1 mol thio ; 127g iodine mol ; g ; 0.508g 0.9g of oil react with 0.504g iodine 100g of oil react with = 56 /56.4 [3] (iii) stearic acid is saturated (less iodine reacts) [1]

163 (d) (i) carbon dioxide [1] water/steam [1] (ii) carbon/carbon monoxide [1] (iii) 2 from 3: carbon dioxide global warming carbon smoke/soot carbon monoxide poisonous/toxic (a) (i) 2NH 3 + H 2 SO 4 (NH 4 ) 2 SO 4 (ii) NH 3 is a proton acceptor [1] (b) (i) methyl orange [1] (ii) the vertical section of the titration curve is on the acid side /ammonium sulphate is acidic methyl orange changes colour at low ph [1] (c) K b = [NH + = 4 ] [OH ] = [NH 3 ] [OH ] [OH ] 2 = = [OH ] = = [H + ] [OH ] = [H + ] = [H + ] = = ph = [4] (d) (i) NH 3 + CH 3 CO 2 H CH 3 CO 2 NH 4 [1] (ii) 2 from 3: no vertical section on titration curve (1) no definite colour change/no sharp end-point (1) weak acid with weak base (1) 12 Section B 70 Total 90

164 New Specification ADVANCED General Certificate of Education January 2010 Chemistry Assessment Unit A2 1 assessing Periodic Trends and Further Organic, Physical and Inorganic Chemistry [AC211] WEDNESDAY 27 JANUARY, MORNING TIME 2 hours. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all fifteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all five questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 120. Quality of written communication will be assessed in Question 11(d)(i). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

165 Section A For each of the following questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 Which one of the following substances, when added to water in equimolar amounts, will form the solution with the highest ph? A B C D ammonium chloride ammonium ethanoate potassium ethanoate potassium chloride 2 Which one of the following substances has a different molecular formula from its empirical formula? A B C D butanoic acid ethanal propanal propanone 3 Zinc is manufactured by the reduction of its oxide using carbon. H = +237 kj mol 1 S = +190 J K 1 mol 1 ZnO(s) + C(s) Zn(s) + CO(g) What is the minimum temperature needed for this reaction to become feasible? A B C D 154 K 427 K 975 K 1248 K 4 How many isomers which have the molecular formula C 3 H 6 O can be reduced by lithal to an alcohol? A 1 B 2 C 3 D 4 [Turn over

166 5 Which one of the following compounds contains co-ordinate (dative) bonds? A Al 2 Cl 6 B CCl 4 C MgCl 2 D NaCl 6 The bromine clock reaction proceeds according to the equation: 6H + (aq) + 5Br (aq) + BrO 3 (aq) 3Br 2 (aq) + 3H 2 O(l) The rate equation is: Rate = k[h + ] 2 [Br ][BrO 3 ] When the rate of disappearance of bromide ions is mol dm 3 s 1, which one of the following statements is correct? A The rate of disappearance of bromate(v) ions, BrO 3, is mol dm 3 s 1. B The rate of disappearance of bromate(v) ions, BrO 3, is mol dm 3 s 1. C The rate of disappearance of hydrogen ions is mol dm 3 s 1. D The rate of disappearance of hydrogen ions is mol dm 3 s 1 7 In which one of the following do all three oxides behave as indicated at room temperature? neutralises dilute acid neutralises dilute alkali dissolves in water to form an acidic solution A Na 2 O MgO SiO 2 B MgO Al 2 O 3 Cl 2 O 7 C P 4 O 10 SiO 2 SO 3 D Al 2 O 3 SO 2 Na 2 O

167 8 The diagram shows the distribution of a substance X between ether and water at equilibrium. 75 cm 3 of water containing 0.83 g of X 10 cm 3 of ether containing 3.28 g of X What is the value of the partition coefficient K d = [X in ether]? [X in water] A 3.95 B 7.50 C D Which one of the following would not be affected by boiling with aqueous sodium hydroxide? A B C D ethyl ethanoate glycerol olive oil propanoic acid 10 What is the ph of a solution containing 6.0 g of ethanoic acid, CH 3 COOH (K a = moldm 3 ), and 2.0 g of sodium ethanoate, CH 3 COONa, dissolved in 100 cm 3 of solution? A 2.38 B 4.15 C 4.28 D 4.76

168 Section B Answer all five questions in the spaces provided. 11 Formaldehyde (methanal), HCHO, is a colourless gas which is readily soluble in water. The aqueous solution is used for preserving anatomical specimens. (a) Explain why formaldehyde is soluble in water. (b) Formaldehyde is a reducing agent as illustrated by its reaction with Tollen s reagent. (i) Write an equation for the oxidation of formaldehyde using [O] to represent the oxidising agent. [1] (ii) Write the half-equation for the reduction of silver ions in Tollen s reagent. [1] (iii) What is observed during this reaction? [1] (c) Formaldehyde reacts with hydrogen cyanide. Draw a flow scheme for the mechanism of this reaction. [3]

169 (d) Methanoic acid undergoes an acid catalysed reaction with bromine according to the equation: Br 2 (aq) + HCOOH(aq) H+ (aq) 2Br - (aq) + 2H + (aq) + CO 2 (g) (i) Suggest an experimental method to investigate the rate of this reaction. How would you find the order of the reaction with respect to bromine? Quality of written communication [4] (ii) The rate law was found to be Rate = k[br 2 ][HCOOH] Deduce the units for the rate constant k. [1] (iii) On the axes below, sketch the expected shape of the graphs in this reaction. [HCOOH] rate time [HCOOH]

170 (e) Methanoic acid reacts with ethanol in the presence of concentrated sulphuric acid to form an ester. (i) Write the equation for this esterification. (ii) Name the ester formed. [1] (iii) State two functions of concentrated sulphuric acid in this reaction.

171 12 The combustion of non-renewable hydrocarbon fuels has contributed to the increase in the atmospheric concentration of carbon dioxide. This in turn is believed to be a key factor in global warming. (a) Carbon dioxide absorbs infra-red radiation. State two effects this radiation has on the bonds in a carbon dioxide molecule. (b) Photosynthesis involves conversion of carbon dioxide and water into a carbohydrate and oxygen. (i) Write an equation for photosynthesis representing the carbohydrate as C 6 H 12 O 6. [1] (ii) A mature tree can produce approximately 220 kg of oxygen per year. What volume of carbon dioxide, measured at one atmosphere pressure and 20 ºC, does a tree need to produce this mass of oxygen? [3] (iii) Wood is approximately 50% cellulose. Burning wood releases carbon dioxide into the atmosphere. Write an equation for the complete combustion of cellulose. Use the formula C 6 H 10 O 5 to represent cellulose. (c) The oceans play an important part in determining the percentage of carbon dioxide in the atmosphere. It is estimated that the oceans contain some tonnes of carbon in total. Calculate the mass of carbon dioxide which the oceans have absorbed to contain this mass of carbon.

172 (d) Carbon dioxide dissolves in water according to the equation: CO 2 (g) + aq CO 2 (aq) Equilibrium 1 Approximately 4% of the dissolved carbon dioxide reacts with water to form hydrogencarbonate ions and hydrogen ions in a further equilibrium. CO 2 (aq) + H 2 O(l) HCO 3 (aq) + H + (aq) Equilibrium 2 (i) Explain the effect a rise in atmospheric carbon dioxide levels would have on the position of Equilibrium 1. [1] (ii) Write an expression for the equilibrium constant, K c, for Equilibrium 2. [1] (iii) A solution of carbon dioxide is weakly acidic. Explain whether the value of K c will be large or small. [1]

173 13 Ketones and carboxylic acids are produced by the oxidation of alcohols. (a) The identity of an unknown ketone was determined by preparing the solid derivative from 2,4-dinitrophenylhydrazine and determining the melting point of the purified product. (i) Write the equation for the reaction of butanone with 2,4-dinitrophenylhydrazine. [3] (ii) State the expected colour of the solid derivative. [1] (iii) Describe how you would purify the solid derivative. [3] (iv) Describe how the melting point of the purified solid would be determined experimentally. [3] (v) What two effects would impurities have on the recorded melting point?

174 (b) Lactic acid, CH 3 CHOHCOOH, is a weak acid which builds up in muscles during exercise. The molecule is optically active. (i) Explain the term optically active. (ii) Draw the 3D structures of the two chiral isomers. (c) In an experiment to determine the percentage by mass of lactic acid in an aqueous solution, 25.0 cm 3 samples of the acid solution were titrated against 1 mol dm 3 sodium hydroxide solution. The average titre was found to be 24.3 cm 3. (i) Write the equation for the reaction of lactic acid with sodium hydroxide. (ii) Calculate the molarity of the lactic acid solution. [1] (iii) Calculate the concentration of the lactic acid solution in g dm 3. [3] (iv) Name a suitable indicator for this titration. [1]

175 (d) A carboxylic acid was found to contain 58.7% carbon, 9.8% hydrogen and 31.5% oxygen. Deduce the empirical formula of the acid. [3] (e) Fats and oils are triesters of glycerol and long chain carboxylic acids. The fat contained in mutton is predominantly a triester formed from stearic acid, CH 3 (CH 2 ) 16 COOH. (i) Draw the structure of this triester. (ii) The saponification value of a fat provides information about the structure. Define the term saponification value and explain what a high value would indicate about a fat. [4] [Turn over

176 14 structure: CH 2 COOH HO C COOH CH 2 COOH (a) (i) How many asymmetric (chiral) centres are present in the molecule? [1] (ii) The partially completed systematic name for citric acid is given below. Complete the name by inserting commas and hyphens in the appropriate spaces. 2 hydroxypropane tricarboxylic acid (b) Citric acid reacts with sodium hydrogencarbonate in an endothermic reaction. The expression G = H T S can be used to explain why endothermic processes can proceed spontaneously. (i) Write the equation for the reaction of citric acid with excess sodium hydrogencarbonate. (ii) State one observation which would indicate the reaction was complete. [1] (iii) Explain the meaning of the symbol S.

177 (iv) Explain, in terms of the expression G = H T S, why the reaction of citric acid with sodium hydrogencarbonate proceeds spontaneously despite being endothermic. (c) The first acid dissociation constant, K a, for citric acid is mol dm 3. (i) Write an equation for the first ionisation of citric acid in aqueous solution. [1] (ii) Write an expression for the first acid dissociation constant, K a, for citric acid using RCOOH to represent citric acid. [1] (iii) Calculate the ph of a 0.1 mol dm 3 solution of citric acid assuming only the first ionisation takes place. [3] [Turn over

178 15 Compounds containing fluorine find diverse uses including polymer manufacture and additives for toothpaste. (a) The polymer Teflon, polytetrafluoroethene, is made by polymerising tetrafluoroethene which itself is produced from chlorodifluoromethane according to the equation: 2CHClF 2 (g) C 2 F 4 (g) + 2HCl(g) H = +128 kj mol 1 (i) State and explain the effect of increasing the overall pressure on the yield of tetrafluoroethene. (ii) State and explain the effect of increasing the temperature on the yield of tetrafluoroethene. (iii) 0.2 mole of chlorodifluoromethane was placed in a 5 dm 3 sealed flask and heated. At equilibrium the mixture obtained contained only 0.04 mole of the gas. Calculate the value of K c for this reaction and state its units. [4] (iv) State two advantages of polymer disposal by incineration compared to landfill.

179 (b) Sodium fluoride is added to toothpaste to reduce tooth decay. The partially completed Born-Haber cycle for sodium fluoride is shown below. Na + (g) + F (g) NaF(s) (i) Complete the empty boxes above by inserting the appropriate chemical symbols. [4] (ii) Using the data below, calculate the lattice enthalpy for sodium fluoride. kj mol 1 First ionisation energy of sodium +496 Enthalpy of atomisation of sodium +107 Bond enthalpy of fluorine +158 Electron affinity of fluorine 333 Enthalpy of formation of sodium fluoride 574 (iii) Write the electronic configuration in s, p and d notation for a sodium ion, Na +, and a fluoride ion, F. sodium ion fluoride ion

180 New Specifi cation ADVANCED General Certificate of Education January 2010 Chemistry Assessment Unit A2 1 assessing Periodic Trends and Further Organic, Physical and Inorganic Chemistry [AC211] WEDNESDAY 27 JANUARY, MORNING Standardising Meeting Version MARK SCHEME