(4) Suggest how a student doing this experiment could check that all the water had been removed

Transcription

1 A sample of hydrated nickel sulfate (NiSO 4.xH 2 O) with a mass of g was heated to remove all water of crystallisation. The solid remaining had a mass of.344 g. (a) Calculate the value of the integer x. Show your working. (4) (b) Suggest how a student doing this experiment could check that all the water had been removed. (2) (Total 6 marks) Page of 2

2 2 Some airbags in cars contain sodium azide (NaN 3 ). (a) Sodium azide is made by reacting dinitrogen monoxide gas with sodium amide (NaNH 2 ) as shown by the equation. 2NaNH 2 + N 2 O NaN 3 + NaOH + NH 3 Calculate the mass of sodium amide needed to obtain 550 g of sodium azide, assuming there is a 95.0% yield of sodium azide. Give your answer to 3 significant figures. (5) Page 2 of 2

3 (b) If a car is involved in a serious collision, the sodium azide decomposes to form sodium and nitrogen as shown in the equation. 2NaN 3 (s) 2Na(s) + 3N 2 (g) The nitrogen produced then inflates the airbag to a volume of m 3 at a pressure of 50 kpa and temperature of 35 C. Calculate the minimum mass of sodium azide that must decompose. (The gas constant R = 8.3 J K mol ) (6) Page 3 of 2

4 (c) Sodium azide is toxic. It can be destroyed by reaction with an acidified solution of nitrous acid (HNO 2 ) as shown in the equation. 2NaN 3 + 2HNO 2 + 2HCl 3N 2 + 2NO + 2NaCl + 2H 2 O (i) A 500 cm 3 volume of the nitrous acid solution was used to destroy completely 50 g of the sodium azide. Calculate the concentration, in mol dm 3, of the nitrous acid used. (3) (ii) Nitrous acid decomposes on heating. Balance the following equation for this reaction....hno 2...HNO NO +...H 2 O () (d) Sodium azide has a high melting point. Predict the type of bonding in a crystal of sodium azide. Suggest why its melting point is high. Type of bonding... Reason for high melting point... (3) Page 4 of 2

5 (e) The azide ion has the formula N 3 (i) The azide ion can be represented as N N N One of these bonds is a co ordinate bond. On the following diagram, draw an arrowhead on one of the bonds to represent the direction of donation of the lone pair in the co ordinate bond. N N N () (ii) Give the formula of a molecule that has the same number of electrons as the azide ion. () (iii) Which is the correct formula of magnesium azide? Tick ( ) one box. Mg 3 N MgN MgN 6 Mg 3 N 2 () (Total 2 marks) Page 5 of 2

6 3 Zinc is similar to Group 2 metals and forms compounds containing Zn 2+ ions. Write an equation for the thermal decomposition of zinc carbonate to zinc oxide. Calculate the percentage atom economy for the formation of zinc oxide from zinc carbonate in this reaction. Equation Percentage atom economy (Total 3 marks) 4 Calamine lotion can contain a mixture of zinc carbonate and zinc oxide in suspension in water. A manufacturer of calamine lotion claims that a sample contains 5.00 g of zinc carbonate and 5.00 g of zinc oxide made up to 00 cm 3 with distilled water. (a) A chemist wanted to check the manufacturer s claim. The chemist took a 20.0 cm 3 sample of the calamine lotion and added it to an excess of sulfuric acid. The volume of carbon dioxide evolved was measured over time. The chemist s results are shown in the table. Time / s Volume / cm (i) (ii) Plot a graph of the results in the table on the grid. The volume should be on the y-axis. Draw a best-fit curve through all the points. Estimate the time taken for the reaction to be completed. (3) () Page 6 of 2

7 (b) (i) The volume of carbon dioxide in part (a) was measured at 293 K and at a pressure of 00 kpa. Use information from your graph to calculate the maximum amount, in moles, of carbon dioxide evolved from the zinc carbonate in this 20.0 cm 3 sample. The gas constant, R = 8.3 J K mol Show your working. (3) (ii) Use your answer to part (i) to calculate the mass of zinc carbonate in the 20.0 cm 3 sample of calamine lotion. (If you were unable to complete part (i), you may assume that the amount of carbon dioxide evolved was mol. This is not the correct answer.) (2) (iii) Calculate the difference between your answer to part (ii) and the manufacturer s claim that there are 5.00 g of zinc carbonate in 00 cm 3 of the calamine lotion. Express this difference as a percentage of the manufacturer s claim. (If you were unable to complete part (ii), you may assume that the mass of zinc carbonate in the 20 cm 3 sample of calamine lotion was 2.87 g. This is not the correct answer.) Difference... Percentage... (2) Page 7 of 2

8 5 (c) (a) Draw a diagram of a suitable apparatus needed to perform the experiment outlined in part (a). Include in your diagram a method for collecting and measuring the carbon dioxide. The apparatus should be airtight. (2) (Total 3 marks) Suggest one reason why sugars are often added to antacid tablets. () (b) In one titration, a student added significantly more phenolphthalein than instructed. The volume of sodium hydroxide solution in this titration was greater than the average value of the concordant titres. State a property of the indicator that would explain this result. () (c) Some other types of antacid tablets contain carbonate ions. Suggest why this may be a disadvantage when used as a medicine to relieve indigestion. () (Total 3 marks) 6 A teacher noticed that a student had not cleared a large air bubble from below the burette tap in preparing the burette for use before starting the titration. This air bubble was ejected during the first titration of the volumetric flask mixture. (a) State the effect that this mistake would have on the value of the first titre. () Page 8 of 2

9 (b) State and explain the effect, if any, that this mistake would have on the average titre for this experiment. (2) (Total 3 marks) 7 When boric acid (H 3 BO 3 ) is applied as a coating on wood, it acts as a fire retardant by decreasing the rate of combustion. Thermal decomposition of boric acid takes place in two stages. In an experiment a sample of boric acid was heated in a crucible at 70 C. The results of this experiment are given in the table. Time of heating / minutes Mass of crucible and contents / g Page 9 of 2

10 Plot a graph of the results from the table above to show the mass of the crucible and boric acid (y-axis) against time of heating on the grid. (Total 4 marks) Page 0 of 2

11 8 A green solution, X, is thought to contain [Fe(H 2 O) 6 ] 2+ ions. (a) The presence of these ions can be confirmed by reacting separate samples of solution X with aqueous ammonia and with aqueous sodium carbonate. Write equations for each of these reactions and describe what you would observe. (4) (b) A 50.0 cm 3 sample of solution X was added to 50 cm 3 of dilute sulfuric acid and made up to 250 cm 3 of solution in a volumetric flask. A 25.0 cm 3 sample of this solution from the volumetric flask was titrated with a mol dm 3 solution of KMnO 4 At the end point of the reaction, the volume of KMnO 4 solution added was 8.70 cm 3. (i) State the colour change that occurs at the end point of this titration and give a reason for the colour change. (2) Page of 2

12 (ii) Write an equation for the reaction between iron(ii) ions and manganate(vii) ions. Use this equation and the information given to calculate the concentration of iron(ii) ions in the original solution X. (5) (Total marks) Page 2 of 2

13 9 N-phenylethanamide is used as an inhibitor in hydrogen peroxide decomposition and also in the production of dyes. N-phenylethanamide can be produced in a laboratory by the reaction between phenylammonium sulfate and an excess of ethanoic anhydride: (a) A student carried out this preparation using.5 g of phenylammonium sulfate (M r = 284.) and excess ethanoic anhydride. (i) Calculate the maximum theoretical yield of N phenylethanamide that could be produced in the reaction. Record your answer to an appropriate precision. Show your working. (3) (ii) In the preparation, the student produced 0.89 g of N phenylethanamide. Calculate the percentage yield for the reaction. () Page 3 of 2

14 (b) The student purified the crude solid product, N phenylethanamide, by recrystallisation. (i) Outline the method that the student should use for this recrystallisation. (4) (ii) Outline how you would carry out a simple laboratory process to show that the recrystallised product is a pure sample of N phenylethanamide. (3) (iii) Assume that the reaction goes to completion. Suggest two practical reasons why the percentage yield for this reaction may not be 00% (2) Page 4 of 2

15 (c) The reaction to form N phenylethanamide would happen much more quickly if the student used ethanoyl chloride instead of ethanoic anhydride. Explain why the student might prefer to use ethanoic anhydride, even though it has a slower rate of reaction. (2) (Total 5 marks) 0 In a titration experiment, a good technique is essential for an accurate result to be obtained. (a) Suggest a reason for removing the funnel after it has been used for filling the burette. () (b) Suggest one other source of error in using the burette to carry out a titration. () (c) During the titration, the inside of the conical flask is rinsed with distilled water. Suggest why rinsing improves the accuracy of the titre. () (d) Explain why adding this extra water does not change the volume of EDTA solution that is required in the titration. () (Total 4 marks) Page 5 of 2

16 The maximum errors for the pipette and the burette are shown below. These errors take into account multiple measurements. Pipette ± 0.05 cm 3 Burette ± 0.5 cm 3 Estimate the maximum percentage error in using each of these pieces of apparatus. Use an average titre cm 3 to calculate the percentage error in using the burette. Show your working. Pipette Burette (Total 2 marks) 2 This question is about the elements in Group 2 and their compounds. (a) Use the Periodic Table to deduce the full electron configuration of calcium. () (b) Write an ionic equation, with state symbols, to show the reaction of calcium with an excess of water. () (c) State the role of water in the reaction with calcium. () (d) Write an equation to show the process that occurs when the first ionisation energy of calcium is measured. () Page 6 of 2

17 (e) State and explain the trend in the first ionisation energies of the elements in Group 2 from magnesium to barium. Trend... Explanation... (3) (Total 7 marks) 3 (a) Write an equation, including state symbols, for the reaction with enthalpy change equal to the standard enthalpy of formation for CF 4 (g). () (b) Explain why CF 4 has a bond angle of (2) Page 7 of 2

18 (c) Table gives some values of standard enthalpies of formation (Δ f H ϴ ). Table Substance F 2 (g) CF 4 (g) HF(g) Δ f H ϴ / kj mol The enthalpy change for the following reaction is 2889 kj mol. C 2 H 6 (g) + 7F 2 (g) 2CF 4 (g) + 6HF(g) Use this value and the standard enthalpies of formation in Table to calculate the standard enthalpy of formation of C 2 H 6 (g). Standard enthalpy of formation of C 2 H 6 (g) =... kj mol (3) Page 8 of 2

19 (d) Methane reacts violently with fluorine according to the following equation. CH 4 (g) + 4F 2 (g) CF 4 (g) + 4HF(g) ΔH = 904 kj mol Some mean bond enthalpies are given in Table 2. Table 2 Bond C H C F H F Mean bond enthalpy / kj mol A student suggested that one reason for the high reactivity of fluorine is a weak F F bond. Is the student correct? Justify your answer with a calculation using these data. (4) (Total 0 marks) Page 9 of 2

20 4 This question is about reactions of calcium compounds. (a) A pure solid is thought to be calcium hydroxide. The solid can be identified from its relative formula mass. The relative formula mass can be determined experimentally by reacting a measured mass of the pure solid with an excess of hydrochloric acid. The equation for this reaction is Ca(OH) 2 + 2HCl CaCl 2 + 2H 2 O The unreacted acid can then be determined by titration with a standard sodium hydroxide solution. You are provided with 50.0 cm 3 of mol dm 3 hydrochloric acid. Outline, giving brief practical details, how you would conduct an experiment to calculate accurately the relative formula mass of the solid using this method. (8) Page 20 of 2

21 (b) A 3.56 g sample of calcium chloride was dissolved in water and reacted with an excess of sulfuric acid to form a precipitate of calcium sulfate. The percentage yield of calcium sulfate was 83.4%. Calculate the mass of calcium sulfate formed. Give your answer to an appropriate number of significant figures. Mass of calcium sulfate formed =... g (3) (Total marks) 5 A sample of pure Mg(NO 3 ) 2 was decomposed by heating as shown in the equation below. 2Mg(NO 3 ) 2 (s) 2MgO(s) + 4NO 2 (g) + O 2 (g) (a) A g sample of Mg(NO 3 ) 2 was completely decomposed by heating. Calculate the total volume, in cm 3, of gas produced at 60.0 C and 00 kpa. Give your answer to the appropriate number of significant figures. The gas constant R = 8.3 J K mol. Total volume of gas =... cm 3 (5) (b) The mass of MgO obtained in this experiment is slightly less than that expected from the mass of Mg(NO 3 ) 2 used. Suggest one practical reason for this. () (Total 6 marks) Page 2 of 2

22 6 Which of these pieces of apparatus has the lowest percentage uncertainty in the measurement shown? A B C D Volume of 25 cm 3 measured with a burette with an uncertainty of ±0. cm 3. Volume of 25 cm 3 measured with a measuring cylinder with an uncertainty of ±0.5 cm 3. Mass of 0.50 g measured with a balance with an uncertainty of ±0.00 g. Temperature change of 23.2 C measured with a thermometer with an uncertainty of ±0. C. (Total mark) 7 A student is provided with a 5.00 cm 3 sample of mol dm 3 hydrochloric acid. The student is asked to devise a method to prepare a hydrochloric acid solution with a concentration of mol dm 3 by diluting the sample with water. Which of these is the correct volume of water that should be added? A 45.0 cm 3 B 95.0 cm 3 C 00 cm 3 D 995 cm 3 (Total mark) 8 Which of the following contains the most chloride ions? A B C D 0 cm 3 of mol dm 3 aluminium chloride solution 20 cm 3 of mol dm 3 calcium chloride solution 30 cm 3 of mol dm 3 hydrochloric acid 40 cm 3 of mol dm 3 sodium chloride solution (Total mark) Page 22 of 2

23 9 Compound J, known as leaf alcohol, has the structural formula CH 3 CH 2 CH=CHCH 2 CH 2 OH and is produced in small quantities by many green plants. The E isomer of J is responsible for the smell of freshly cut grass. (a) Give the structure of the E isomer of J. () (b) Give the skeletal formula of the organic product formed when J is dehydrated using concentrated sulfuric acid. () Page 23 of 2

24 (c) Another structural isomer of J is shown below. Explain how the Cahn-Ingold-Prelog (CIP) priority rules can be used to deduce the full IUPAC name of this compound. (6) Page 24 of 2

25 (d) The effect of gentle heat on maleic acid is shown below. A student predicted that the yield of this reaction would be greater than 80%. In an experiment,0.0 g of maleic acid were heated and 6.53 g of organic product were obtained. Is the student correct? Justify your answer with a calculation using these data. (2) (Total 0 marks) 20 Glucose can decompose in the presence of microorganisms to form a range of products. One of these is a carboxylic acid (M r = 88.0) containing 40.9% carbon and 4.5% hydrogen by mass. (a) Deduce the empirical and molecular formulas of the carboxylic acid formed. Empirical formula =... Molecular formula =... (4) (b) Ethanol is formed by the fermentation of glucose. A student carried out this fermentation reaction in a beaker using an aqueous solution of glucose at a temperature of 25 C in the presence of yeast. Write an equation for the reaction occurring during fermentation. () Page 25 of 2

26 (c) In industry, this fermentation reaction is carried out at 35 C rather than 25 C. Suggest one advantage and one disadvantage for industry of carrying out the fermentation at this higher temperature. Advantage... Disadvantage... (2) (d) The method used by the student in part (b) would result in the ethanol being contaminated by ethanoic acid. How does this contamination occur? () (e) Give two differences between the infrared spectrum of a carboxylic acid and that of an alcohol other than in their fingerprint regions. Use Table A on the Data Sheet. Difference... Difference 2... (2) (Total 0 marks) 2 CCl 4 is an effective fire extinguisher but it is no longer used because of its toxicity and its role in the depletion of the ozone layer. In the upper atmosphere, a bond in CCl 4 breaks and reactive species are formed. (a) Identify the condition that causes a bond in CCl 4 to break in the upper atmosphere. Deduce an equation for the formation of the reactive species. Condition... Equation (2) Page 26 of 2

27 (b) One of the reactive species formed from CCl 4 acts as a catalyst in the decomposition of ozone. Write two equations to show how this species acts as a catalyst. Equation Equation 2 (2) (c) A small amount of the freon CF 3 Cl with a mass of kg escaped from a refrigerator, into a room of volume 00 m 3. Assuming that the freon is evenly distributed throughout the air in the room, calculate the number of freon molecules in a volume of 500 cm 3. Give your answer to the appropriate number of significant figures. The Avogadro constant = mol. Number of molecules =... (3) (Total 7 marks) 22 Which of these samples of gas contains the largest number of molecules? The gas constant R = 8.3 J K mol. A B C D m 3 at Pa and 300 K m 3 at Pa and 400 K dm 3 at Pa and 500 K dm 3 at Pa and 600 K (Total mark) Page 27 of 2

28 23 What is the total volume of gas remaining after 20 cm 3 ethane are burned completely in 00 cm 3 oxygen? All volumes are measured at the same pressure and the same temperature, which is above 00 C. C 2 H O 2 2CO 2 + 3H 2 O A 40 cm 3 B 00 cm 3 C 20 cm 3 D 30 cm 3 (Total mark) 24 Isooctane (C 8 H 8 ) is the common name for the branched-chain hydrocarbon that burns smoothly in car engines. The skeletal formula of isooctane is shown below. (a) Give the IUPAC name for isooctane. () (b) Deduce the number of peaks in the 3 C NMR spectrum of isooctane () (c) Isooctane can be formed, together with propene and ethene, in a reaction in which one molecule of an alkane that contains 20 carbon atoms is cracked. Using molecular formulas, write an equation for this reaction. () Page 28 of 2

29 (d) How do the products of the reaction in part (c) show that the reaction is an example of thermal cracking? () (e) Deduce the number of monochloro isomers formed by isooctane. Draw the structure of the monochloro isomer that exists as a pair of optical isomers. Number of monochloro isomers... Structure (2) (f) An isomer of isooctane reacts with chlorine to form only one monochloro compound. Draw the skeletal formula of this monochloro compound. () (g) A sample of a monochlorooctane is obtained from a comet. The chlorine in the monochlorooctane contains the isotopes 35 Cl and 37 Cl in the ratio.5 :.0 Calculate the M r of this monochlorooctane. M r =... (2) Page 29 of 2

30 (h) Isooctane reacts with an excess of chlorine to form a mixture of chlorinated compounds. One of these compounds contains 24.6% carbon and 2.56% hydrogen by mass. Calculate the molecular formula of this compound. Molecular formula =... (3) (Total 2 marks) 25,4-diaminobenzene is an important intermediate in the production of polymers such as Kevlar and also of polyurethanes, used in making foam seating. A possible synthesis of,4-diaminobenzene from phenylamine is shown in the following figure. Page 30 of 2

31 (a) A suitable reagent for step is CH 3 COCl Name and draw a mechanism for the reaction in step. Name of mechanism... Mechanism (5) (b) The product of step was purified by recrystallisation as follows. The crude product was dissolved in the minimum quantity of hot water and the hot solution was filtered through a hot filter funnel into a conical flask. This filtration removed any insoluble impurities. The flask was left to cool to room temperature. The crystals formed were filtered off using a Buchner funnel and a clean cork was used to compress the crystals in the funnel. A little cold water was then poured through the crystals. After a few minutes, the crystals were removed from the funnel and weighed. A small sample was then used to find the melting point. Give reasons for each of the following practical steps. The minimum quantity of hot water was used The flask was cooled to room temperature before the crystals were filtered off The crystals were compressed in the funnel Page 3 of 2

32 A little cold water was poured through the crystals (4) (c) The melting point of the sample in part (b) was found to be slightly lower than a data-book value. Suggest the most likely impurity to have caused this low value and an improvement to the method so that a more accurate value for the melting point would be obtained. (2) The figure above is repeated here to help you answer the following questions. Page 32 of 2

33 (d) In an experiment starting with 5.05 g of phenylamine, 4.82 g of purified product were obtained in step. Calculate the percentage yield in this reaction. Give your answer to the appropriate number of significant figures. Percentage yield =...% (3) (e) A reagent for step 2 is a mixture of concentrated nitric acid and concentrated sulfuric acid, which react together to form a reactive intermediate. Write an equation for the reaction of this intermediate in step 2. () (f) Name a mechanism for the reaction in step 2. () (g) Suggest the type of reaction occurring in step 3. () (h) Identify the reagents used in step 4. () (Total 8 marks) 26 Ethanedioic acid is a weak acid. Ethanedioic acid acts, initially, as a monoprotic acid. Page 33 of 2

34 (a) Use the concept of electronegativity to justify why the acid strengths of ethanedioic acid and ethanoic acid are different. (6) (b) A buffer solution is made by adding mol of sodium hydroxide to a solution containing.00 0 mol of ethanedioic acid (H 2 C 2 O 4 ). Assume that the sodium hydroxide reacts as shown in the following equation and that in this buffer solution, the ethanedioic acid behaves as a monoprotic acid. H 2 C 2 O 4 (aq) + OH (aq) HC 2 O 4 (aq) + H 2 O(l) The dissociation constant K a for ethanedioic acid is mol dm 3. Calculate a value for the ph of the buffer solution. Give your answer to the appropriate number of significant figures. ph =... (5) Page 34 of 2

35 (c) In a titration, the end point was reached when 25.0 cm 3 of an acidified solution containing ethanedioic acid reacted with cm 3 of mol dm 3 potassium manganate(vii) solution. Deduce an equation for the reaction that occurs and use it to calculate the original concentration of the ethanedioic acid solution. Equation... Calculation Original concentration =... mol dm -3 (4) (Total 5 marks) 27 A sample of 2.8 g of oxygen gas has a volume of 870 cm 3 at a pressure of 0 kpa. What is the temperature of the gas? The gas constant is R = 8.3 J K mol. A 67 K B 334 K C 668 K D K (Total mark) Page 35 of 2

36 28 An ester is hydrolysed as shown by the following equation. RCOOR / + H 2 O RCOOH + R / OH What is the percentage yield of RCOOH when 0.50 g of RCOOH (M r = 00) is obtained from.0 g of RCOOR / (M r = 50)? A 33% B 50% C 67% D 75% (Total mark) 29 A saturated aqueous solution of magnesium hydroxide contains g of Mg(OH) 2 in 00 cm 3 of solution. In this solution, the magnesium hydroxide is fully dissociated into ions. What is the concentration of Mg 2+ (aq) ions in this solution? A mol dm 3 B mol dm 3 C mol dm 3 D mol dm 3 (Total mark) Page 36 of 2

37 30 Magnesium reacts with hydrochloric acid according to the following equation. Mg + 2HCl MgCl 2 + H 2 A student calculated the minimum volume of 2.56 mol dm 3 hydrochloric acid required to react with an excess of magnesium to form 5.46 g of magnesium chloride (M r = 95.3). Which of the following uses the correct standard form and the appropriate number of significant figures to give the correct result of the calculation? A dm 3 B dm 3 C dm 3 D dm 3 (Total mark) 3 In an experiment to identify a Group 2 metal (X), 0.02 g of X reacts with an excess of aqueous hydrochloric acid according to the following equation. X + 2HCl XCl 2 + H 2 The volume of hydrogen gas given off is 65 cm 3 at 99 kpa pressure and 303 K. The gas constant is R = 8.3 J K mol. Which is X? A Barium B Calcium C Magnesium D Strontium (Total mark) Page 37 of 2

38 32 The following equation represents the oxidation of vanadium(iv) ions by manganate(vii) ions in acid solution. 5V 4+ + MnO 4 + 8H + 5V 5+ + Mn H 2 O What volume of mol dm 3 KMnO 4 solution is required to oxidise completely a solution containing 0.00 mol of vanadium(iv) ions? A 0 cm 3 B 25 cm 3 C 50 cm 3 D 00 cm 3 (Total mark) 33 (a) Table shows some data about fundamental particles in an atom. Table Particle proton neutron electron Mass / g (i) An atom of hydrogen can be represented as H Use data from Table to calculate the mass of this hydrogen atom. () (ii) Which one of the following is a fundamental particle that would not be deflected by an electric field? A B C electron neutron proton Write the correct letter, A, B or C, in the box. () Page 38 of 2

39 (b) A naturally occurring sample of the element boron has a relative atomic mass of 0.8. In this sample, boron exists as two isotopes, 0 B and B (i) Calculate the percentage abundance of 0 B in this naturally occurring sample of boron. (2) (ii) State, in terms of fundamental particles, why the isotopes 0 B and B have similar chemical reactions. () (c) Complete Table 2 by suggesting a value for the third ionisation energy of boron. Table 2 First Second Third Fourth Fifth Ionisation energy / kj mol () (d) Write an equation to show the process that occurs when the second ionisation energy of boron is measured. Include state symbols in your equation. () (e) Explain why the second ionisation energy of boron is higher than the first ionisation energy of boron. () (Total 8 marks) Page 39 of 2

40 34 When heated, iron(iii) nitrate (M r = 24.8) is converted into iron(iii) oxide, nitrogen dioxide and oxygen. 4Fe(NO 3 ) 3 (s) 2Fe 2 O 3 (s) + 2NO 2 (g) + 3O 2 (g) A 2.6 g sample of iron(iii) nitrate was completely converted into the products shown. (a) (i) Calculate the amount, in moles, of iron(iii) nitrate in the 2.6 g sample. Give your answer to 3 significant figures. () (ii) Calculate the amount, in moles, of oxygen gas produced in this reaction. () (iii) Calculate the volume, in m 3, of nitrogen dioxide gas at 293 C and 00 kpa produced from 2.6 g of iron(iii) nitrate. The gas constant is R = 8.3 JK mol. (If you have been unable to obtain an answer to part (i), you may assume the number of moles of iron(iii) nitrate is This is not the correct answer.) (4) (b) Suggest a name for this type of reaction that iron(iii) nitrate undergoes. () Page 40 of 2

41 (c) Suggest why the iron(iii) oxide obtained is pure. Assume a complete reaction. () (Total 8 marks) 35 (a) Calcium phosphate reacts with aqueous nitric acid to produce phosphoric acid and calcium nitrate as shown in the equation. Ca 3 (PO 4 ) 2 + 6HNO 3 2H 3 PO 4 + 3Ca(NO 3 ) 2 (i) A 7.26 g sample of calcium phosphate reacted completely when added to an excess of aqueous nitric acid to form 38.0 cm 3 of solution. Calculate the concentration, in mol dm 3, of phosphoric acid in this solution. Give your answer to 3 significant figures. (5) (ii) Calculate the percentage atom economy for the formation of calcium nitrate in this reaction. Give your answer to decimal place. (2) Page 4 of 2

42 (b) Write an equation to show the reaction between calcium hydroxide and phosphoric acid to produce calcium phosphate and water. () (c) Calcium dihydrogenphosphate can be represented by the formula Ca(H 2 PO 4 ) x where x is an integer. A 9.76 g sample of calcium dihydrogenphosphate contains 0.7 g of hydrogen, 2.59 g of phosphorus and 5.33 g of oxygen. Calculate the empirical formula and hence the value of x. Show your working. (4) (Total 2 marks) 36 The correct technique can improve the accuracy of a titration. (a) State why it is important to fill the space below the tap in the burette with solution A before beginning an accurate titration. () (b) Suggest one reason why a 250 cm 3 conical flask is preferred to a 250 cm 3 beaker for a titration. () Page 42 of 2

43 (c) During a titration, a chemist rinsed the inside of the conical flask with deionised water. The water used for rinsing remained in the conical flask. (i) Give one reason why this rinsing can improve the accuracy of the end-point. () (ii) Explain why the water used for rinsing has no effect on the accuracy of the titre. () (d) Suggest one reason why repeating a titration makes the value of the average titre more reliable. () (Total 5 marks) 37 The table below shows some information about three hydrochloric acid solutions used to clean bricks and concrete. Cleaner Acid content by mass / % Price per 25dm 3 / Plattern Concrete Acid Dub-Lit Brick Cleaner Conpat Brick Acid Use the data in the table above to determine the cleaner that offers the best value for money, based on acid content. Show your working (Total mark) Page 43 of 2

44 38 Sodium hydroxide is often sold as a concentrated solution containing 2.0 mol dm 3 of sodium hydroxide. Calculate the volume of water that should be added to 0.0 cm 3 of a 2.0 mol dm 3 solution of sodium hydroxide to make a mol dm 3 solution. Show your working (Total 2 marks) 39 (a) Sodium hydroxide can be obtained as a monohydrate (NaOH.H 2 O). When heated, the water of crystallisation is lost, leaving anhydrous sodium hydroxide (NaOH). A chemist weighed a clean, dry crucible. The chemist transferred.0 g of NaOH.H 2 O to the crucible. The crucible and its contents were heated until a constant mass had been reached. The chemist recorded this mass. The experiment was repeated using different masses of the monohydrate. For each experiment, the chemist recorded the original mass of NaOH.H 2 O and the mass of NaOH left after heating. The chemist s results are shown in the table below. Mass of NaOH.H 2 O / g Mass of NaOH / g Page 44 of 2

45 (i) Plot a graph of mass of NaOH.H 2 O (y-axis) against mass of NaOH on the grid. Draw a straight line of best fit on the graph. (3) Page 45 of 2

46 (ii) Use your graph to determine the mass of NaOH.H 2 O needed to form.00 g of NaOH... g () (iii) Use your answer from part (a) (ii) to confirm that the formula of sodium hydroxide monohydrate is NaOH.H 2 O (2) (b) Sodium hydroxide is used to remove grease from metal components. Sodium hydroxide cannot be used to clean components made of aluminium because it reacts with this metal. (i) Balance the equation for the reaction of aqueous sodium hydroxide with aluminium.... NaOH +... Al +... H 2 O... NaAl(OH) 4 + 3H 2 () (ii) In 986, a sealed aluminium tank exploded while being used by mistake for transporting concentrated sodium hydroxide solution. Suggest one reason why the tank exploded. () (c) A strong alkali such as potassium hydroxide is used as the electrolyte in some alkaline batteries for household use. The electrolyte will escape if the battery casing is broken. Suggest one reason why a leak of this electrolyte is hazardous. () (Total 9 marks) Page 46 of 2

47 40 Sodium phosphate and ammonia are formed when ammonium phosphate is heated with sodium hydroxide solution in a conical flask. There is one other product in this reaction. (a) Complete and balance the equation for the reaction of ammonium phosphate with sodium hydroxide. (NH 4 ) 3 PO NaOH Na 3 PO NH (2) (b) Ammonia is an alkaline gas. Describe how you would use a named indicator to show that ammonia gas is released from the flask in this reaction. State the colour change that you would observe. (2) (Total 4 marks) 4 The alcohol 2-methylpropan-2-ol, (CH 3 ) 3 COH, reacts to form esters that are used as flavourings by the food industry. The alcohol can be oxidised to produce carbon dioxide and water. A student carried out an experiment on a pure sample of 2-methylpropan-2-ol to determine its enthalpy of combustion. A sample of the alcohol was placed into a spirit burner and positioned under a beaker containing 50 cm 3 of water. The spirit burner was ignited and allowed to burn for several minutes before it was extinguished. The results for the experiment are shown in Table. Table Initial temperature of the water / C 8. Final temperature of the water / C 45.4 Initial mass of spirit burner and alcohol / g Final mass of spirit burner and alcohol / g Page 47 of 2

48 (a) Use the results from Table to calculate a value for the heat energy released from the combustion of this sample of 2-methylpropan-2-ol. The specific heat capacity of water is 4.8 J K g. Show your working. (2) (b) Calculate the amount, in moles, of 2-methylpropan-2-ol burned in the experiment. Hence calculate a value, in kj mol, for the enthalpy of combustion of 2-methylpropan-2-ol. Show your working. (If you were unable to calculate an answer to part (a), you should assume that the heat energy released was 5580 J. This is not the correct value.) (3) Page 48 of 2

49 (c) An equation for the combustion of 2-methylpropan-2-ol is (CH 3 ) 3 COH(I) + 6O 2 (g) 4CO 2 (g) + 5H 2 O(I) Table 2 contains some standard enthalpy of formation data. Table 2 (CH 3 ) 3 COH(I) O 2 (g) CO 2 (g) H 2 O(I) H f / kj mol Use the data from Table 2 to calculate a value for the standard enthalpy of combustion of 2-methylpropan-2-ol. Show your working. (3) (d) An accurate value for the enthalpy of combustion of 2-methylpropan-2-ol in which water is formed as a gas is 2422 kj mol. Use this value and your answer from part (b) to calculate the overall percentage error in the student s experimental value for the enthalpy of combustion of 2-methylpropan-2-ol. () (e) Suggest one improvement that would reduce errors due to heat loss in the student s experiment. () Page 49 of 2

50 (f) Suggest one other source of error in the student s experiment. Do not include heat loss, apparatus error or student error. () (Total marks) 42 A student carried out an experiment to find the mass of FeSO 4.7H 2 O in an impure sample, X. The student recorded the mass of X. This sample was dissolved in water and made up to 250 cm 3 of solution. The student found that, after an excess of acid had been added, 25.0 cm 3 of this solution reacted with 2.3 cm 3 of a mol dm 3 solution of K 2 Cr 2 O 7 (a) Use this information to calculate a value for the mass of FeSO 4.7H 2 O in the sample of X. (5) Page 50 of 2

51 (b) The student found that the calculated mass of FeSO 4.7H 2 O was greater than the actual mass of the sample that had been weighed out. The student realised that this could be due to the nature of the impurity. Suggest one property of an impurity that would cause the calculated mass of FeSO 4.7H 2 O in X to be greater than the actual mass of X. Explain your answer. (2) (Total 7 marks) 43 One cell that has been used to provide electrical energy is the Daniell cell. This cell uses copper and zinc. (a) The conventional representation for the Daniell cell is Zn(s) Zn 2+ (aq) Cu 2+ (aq) Cu(s) The e.m.f. of this cell under standard conditions is +.0 V. Deduce the half-equations for the reactions occurring at the electrodes. At Zn electrode... At Cu electrode... (2) (b) A Daniell cell was set up using 00 cm 3 of a.0 mol dm 3 copper(ii) sulfate solution. The cell was allowed to produce electricity until the concentration of the copper(ii) ions had decreased to 0.50 mol dm 3. Calculate the decrease in mass of the zinc electrode. Show your working. (3) Page 5 of 2

52 (c) You are provided with the Daniell cell referred to in part (b), including a zinc electrode of known mass. Briefly outline how you would carry out an experiment to confirm your answer to part (b). (3) (Total 8 marks) 44 In a titration, it is important to wash the inside of the titration flask with distilled or deionised water as you approach the end-point. (a) Suggest one reason why it is important to wash the inside of the flask. () (b) Washing with water decreases the concentration of the reagents in the titration flask. Suggest why washing with water does not affect the titre value. () (Total 2 marks) Page 52 of 2

53 45 The mass spectrum of the isotopes of element X is shown in the diagram. m / z (a) Define the term relative atomic mass. (2) (b) Use data from the diagram to calculate the relative atomic mass of X. Give your answer to one decimal place. (3) (c) Identify the ion responsible for the peak at 72 () Page 53 of 2

54 (d) Identify which one of the isotopes of X is deflected the most in the magnetic field of a mass spectrometer. Give a reason for your answer. Isotope... Reason... (2) (e) In a mass spectrometer, the relative abundance of each isotope is proportional to the current generated by that isotope at the detector. Explain how this current is generated. (2) (f) X and Zn are different elements. Explain why the chemical properties of 70 X and 70 Zn are different. () (Total marks) Page 54 of 2

55 46 Zinc forms many different salts including zinc sulfate, zinc chloride and zinc fluoride. (a) People who have a zinc deficiency can take hydrated zinc sulfate (ZnSO 4.xH 2 O) as a dietary supplement. A student heated 4.38 g of hydrated zinc sulfate and obtained 2.46 g of anhydrous zinc sulfate. Use these data to calculate the value of the integer x in ZnSO 4.xH 2 O Show your working. (3) (b) Zinc chloride can be prepared in the laboratory by the reaction between zinc oxide and hydrochloric acid. The equation for the reaction is ZnO + 2HCl ZnCl 2 + H 2 O A mol sample of pure zinc oxide was added to 00 cm 3 of.20 mol dm 3 hydrochloric acid. Calculate the maximum mass of anhydrous zinc chloride that could be obtained from the products of this reaction. (4) Page 55 of 2

56 (c) Zinc chloride can also be prepared in the laboratory by the reaction between zinc and hydrogen chloride gas. Zn + 2HCl ZnCl 2 + H 2 An impure sample of zinc powder with a mass of 5.68 g was reacted with hydrogen chloride gas until the reaction was complete. The zinc chloride produced had a mass of 0.7 g. Calculate the percentage purity of the zinc metal. Give your answer to 3 significant figures. (4) (d) Predict the type of crystal structure in solid zinc fluoride and explain why its melting point is high. (3) (Total 4 marks) Page 56 of 2

57 47 There is an experimental method for determining the number of water molecules in the formula of hydrated sodium carbonate. This method involves heating a sample to a temperature higher than 300 C and recording the change in mass of the sample. The equation for the reaction taking place is Na 2 CO 3.0H 2 O(s) Na 2 CO 3 (s) + 0H 2 O(g) A group of six students carried out this experiment. They each weighed out a sample of hydrated sodium carbonate. They then heated their sample to a temperature higher than 300 C in a crucible for ten minutes and recorded the final mass after the crucible had cooled. Their results are summarised in the table. Student Initial mass / g Final mass / g Page 57 of 2

58 (a) Plot the values of Initial mass (y-axis) against Final mass on the grid below. A graph of these results should include an additional point. Draw a circle on the grid around the additional point that you should include. (4) Page 58 of 2

59 (b) (c) (d) Draw a best-fit straight line for these results that includes your additional point. Identify each student whose experiment gave an anomalous result. All the students carried out the experiment exactly according to this method. Explain why a student that you identified in part (c) obtained an anomalous result. () () (2) (Total 8 marks) 48 Sodium carbonate is manufactured by the Solvay Process. The separate stages involved in this process are shown in this diagram. Page 59 of 2

60 (a) In Reactor, calcium carbonate is decomposed into calcium oxide and carbon dioxide. Despite no significant leakage of carbon dioxide from this decomposition, this part of the process results in an increase in carbon dioxide in the atmosphere. State why this increase in carbon dioxide occurs. () (b) In Reactor 2, sodium chloride solution, carbon dioxide and ammonia react to form sodium hydrogencarbonate and ammonium chloride. Write an equation for this reaction. () (c) Use information from the diagram to deduce an equation for the reaction taking place in Reactor 3. () (d) An equation for the overall reaction in the Solvay Process is 2NaCl(aq) + CaCO 3 (s) Na 2 CO 3 (s) + CaCl 2 (aq) (i) Calculate the percentage atom economy of this reaction to produce sodium carbonate. Show your working. (2) (ii) State what could be done to improve the percentage atom economy of the Solvay Process. () Page 60 of 2

61 (e) Use information from the diagram to suggest why ammonia is not regarded as a raw material in the Solvay Process. () (Total 7 marks) 49 Baking powder contains sodium hydrogencarbonate and an acid or a mixture of acids. One acid that may be in baking powder is 2,3-dihydroxybutanedioic acid. This has the molecular formula C 4 H 6 O 6 and it is often referred to as tartaric acid. (a) Draw the structural formula of tartaric acid. () (b) Write an equation for the reaction of tartaric acid (C 4 H 6 O 6 ) with sodium hydrogencarbonate to form a salt, carbon dioxide and water. () (c) Substances that contain carbonate or hydrogencarbonate ions can be used to confirm the presence of an acid. Identify one other substance that could be used to confirm the presence of acid groups in tartaric acid. State the observation you would make when this other substance is added to an aqueous solution of tartaric acid. Substance... Observation... (2) Page 6 of 2

62 (d) It is known that tartaric acid contains alcohol and carboxylic acid functional groups only. A test can be used to show that tartaric acid contains secondary alcohol groups, not tertiary alcohol groups. (i) Identify a reagent for this test and state the observation you would make for each type of alcohol. Reagent... Observation for secondary alcohol... Observation for tertiary alcohol... (3) (ii) Suggest why this test cannot be used to distinguish between a primary alcohol and a secondary alcohol. () (e) Baking powder usually contains starch. Starch is added to absorb any water vapour that may come into contact with the baking powder when the container is opened. Deduce a reason why this water vapour needs to be absorbed. () (f) Sodium hydrogencarbonate in baking powder forms carbon dioxide during the production of bread and cakes. Suggest one advantage of having an acid in baking powder. () Page 62 of 2

63 (g) Safety information indicates that tartaric acid and its salts can act as muscle toxins. These can cause paralysis and possible death. Suggest one reason why the use of tartaric acid in baking powder is not a hazard to health. () (Total marks) 50 Read the following instructions that describe how to make up a standard solution of a solid in a volumetric flask. Answer the questions which follow. Take a clean 250 cm 3 volumetric flask. Use the balance provided and a clean, dry container, to weigh out the amount of solid required. Tip the solid into a clean, dry 250 cm 3 beaker and add about 00 cm 3 of distilled water. Use a stirring rod to help the solid dissolve, carefully breaking up any lumps of solid with the rod. When the solid has dissolved, pour the solution into the flask using a filter funnel. Add water to the flask until the level rises to the graduation mark. (a) Suggest three further instructions that would improve the overall technique in this account (3) Page 63 of 2

64 (b) In a series of titrations using the solution made up in part (a), a student obtained the following titres (all in cm 3 ). Rough State what this student must do in order to obtain an accurate average titre in this experiment. (2) (Total 5 marks) 5 This question explores some reactions and some uses of cobalt compounds. (a) Ethanal is oxidised to ethanoic acid by oxygen. The equation for this reaction is 2CH 3 CHO + O 2 2CH 3 COOH This redox reaction is slow at room temperature but speeds up in the presence of cobalt compounds. Explain why a cobalt compound is able to act as a catalyst for this process. Illustrate your explanation with two equations to suggest how, in the presence of water and hydrogen ions, Co 3+ and then Co 2+ ions could be involved in catalysing this reaction. (4) Page 64 of 2

65 (b) In aqueous solution, the [Co(H 2 O) 6 ] 2+ ion reacts with an excess of ethane-,2-diamine to form the complex ion Y. (i) Write an equation for this reaction. Explain, in terms of the chelate effect, why the complex ion Y is formed in preference to the [Co(H 2 O) 6 ] 2+ complex ion. (3) (ii) Draw a diagram that shows the shape of the complex ion Y and shows the type of bond between the ethane-,2-diamine molecules and the cobalt. (3) Page 65 of 2

66 (c) Compound Z is a complex that contains only cobalt, nitrogen, hydrogen and chlorine. A solid sample of Z was prepared by reaction of 50 cm 3 of mol dm 3 aqueous cobalt(ii) chloride with ammonia and an oxidising agent followed by hydrochloric acid. When this sample of Z was reacted with an excess of silver nitrate, 4.22 g of silver chloride were obtained. Use this information to calculate the mole ratio of chloride ions to cobalt ions in Z. Give the formula of the complex cobalt compound Z that you would expect to be formed in the preparation described above. Suggest one reason why the mole ratio of chloride ions to cobalt ions that you have calculated is different from the expected value. (5) (Total 5 marks) 52 The triiodomethane reaction is often used as a test for aldehydes and ketones that contain the CH 3 CO group shown. The aldehyde or ketone is reacted with an alkaline solution of iodine. Triiodomethane (CHl 3 ) is formed as a precipitate. Compounds that contain a group that can be oxidised to the CH 3 CO group will also give a positive result in this test. Page 66 of 2

67 (a) State, with a reason, whether or not ethanol will give a positive result in the triiodomethane reaction. () (b) The equation for the reaction of ethanal with an alkaline solution of iodine is CH 3 CHO + 3l 2 + 4NaOH CHl 3 + HCOONa + 3Nal + 3H 2 O In an experiment using this reaction, the yield of triiodomethane (CHl 3 ) obtained by a student was 83.2%. Calculate the minimum mass of iodine that this student would have used to form 0.0 g of triiodomethane. Give your answer to the appropriate precision. Show your working. (5) (c) Triiodomethane can be separated from the reaction mixture by filtration. State one reason why the solid residue is then washed with water after the filtration. () Page 67 of 2

68 (d) State one reason, other than cost or availability, why water is suitable for washing this solid residue after the filtration. () (Total 8 marks) 53 The pigment Cobalt Yellow contains an octahedral complex of cobalt(iii) and nitrate(iii) ions (NO 2 ). Analysis shows that Cobalt Yellow contains 3.0% of cobalt, 8.6% of nitrogen and 25.9% of potassium by mass. The remainder is oxygen. (a) Use these data to calculate the empirical formula of Cobalt Yellow. Show your working. (3) (b) Deduce the structural formula of the cobalt-containing ion in Cobalt Yellow. () (Total 4 marks) 54 Iron(II) ethanedioate is another insoluble solid used as a pigment in paints and glass. It occurs as a dihydrate (FeC 2 O 4.2H 2 O). One procedure used for the preparation of iron(ii) ethanedioate is outlined below. Procedure A 6.95 g sample of hydrated iron(ii) sulfate (FeSO 4.7H 2 O) was added to 00 cm 3 of water in a beaker and stirred until all of the solid dissolved. A 50 cm 3 volume of 0.20 mol dm 3 sodium ethanedioate solution was added to the beaker. The mixture was stirred until precipitation was complete. After filtration, 3.3 g of the dihydrate (FeC 2 O 4.2H 2 O) were collected. (a) Write an equation for the reaction between iron(ii) sulfate and sodium ethanedioate. () Page 68 of 2

69 (b) Calculate the amount, in moles, of FeSO 4.7H 2 O in 6.95 g of hydrated iron(ii) sulfate. Show your working. (2) (c) Calculate the amount, in moles, of sodium ethanedioate in 50 cm 3 of 0.20 mol dm 3 sodium ethanedioate solution. () (d) Calculate the percentage yield of iron(ii) ethanedioate dihydrate (M r = 79.8) formed in this reaction. Give your answer to the appropriate precision. Show your working. (2) (e) In this experiment, no side reactions take place, the reagents are pure and the reaction goes to completion. Suggest one reason why the yield of iron(ii) ethanedioate dihydrate in this experiment is less than 00%. () Page 69 of 2

70 (f) When dissolved in dilute sulfuric acid, the number of moles of ethanedioate ions in a pigment can be determined by titration with acidified potassium manganate(vii). Explain why the titration of a sample of iron(ii) ethanedioate would require a different amount of potassium manganate(vii) than a titration of an equimolar amount of copper(ii) ethanedioate. (2) (Total 9 marks) 55 (a) Because of the toxic nature of the copper(ii) ion, a wide range of alternative anti-fungal drugs has been developed for use in agriculture. One example is Zineb. (i) The negative ion in Zineb could act as a bidentate ligand. On the structure above, draw a ring around each of two atoms that could provide the lone pairs of electrons when this ion acts as a bidentate ligand. () (ii) Calculate the M r of Zineb. Give your answer to the appropriate precision () (iii) Name the functional group formed at each end of the negative ion when all the sulfur atoms in the structure of Zineb are replaced by oxygen atoms.... () Page 70 of 2