Date of birth Day Month Year Scottish candidate number

Transcription

1 FOR OFFIIAL USE X273/2/02 Total Section B NATIONAL QUALIFIATIONS 203 FRIDAY, 3 MAY.00 PM 3.30 PM EMISTRY IGER (REVISED) Fill in these boxes and read what is printed below. Full name of centre Town Fename(s) Surname Date of birth Day Month Year Scottish candidate number Number of seat Reference may be made to the hemistry igher and Advanced igher Data Booklet. SETION A Questions 30 (30 marks) Instructions f completion of Section A are given on page two. F this section of the examination you must use an B pencil. SETION B (70 marks) All questions should be attempted. 2 The questions may be answered in any der but all answers are to be written in the spaces provided in this answer book, and must be written clearly and legibly in ink. 3 Rough wk, if any should be necessary, should be written in this book and then sced through when the fair copy has been written. If further space is required, a supplementary sheet f rough wk may be obtained from the Invigilat. 4 Additional space f answers will be found at the end of the book. If further space is required, supplementary sheets may be obtained from the Invigilat and should be inserted inside the front cover of this book. 5 The size of the space provided f an answer should not be taken as an indication of how much to write. It is not necessary to use all the space. 6 Befe leaving the examination room you must give this book to the Invigilat. If you do not, you may lose all the marks f this paper. LI X273/2/02 6/060 *X273/2/02*

2 203 hemistry igher (Revised) Finalised Marking Instructions Scottish Qualifications Authity 203 The infmation in this publication may be reproduced to suppt SQA qualifications only on a non-commercial basis. If it is to be used f any other purposes written permission must be obtained from SQA s NQ Assessment team. Where the publication includes materials from sources other than SQA (secondary copyright), this material should only be reproduced f the purposes of examination assessment. If it needs to be reproduced f any other purpose it is the centre s responsibility to obtain the necessary copyright clearance. SQA s NQ Assessment team may be able to direct you to the secondary sources. These Marking Instructions have been prepared by Examination Teams f use by SQA Appointed Markers when marking External ourse Assessments. This publication must not be reproduced f commercial trade purposes.

3 Part One: General Marking Principles f hemistry igher (Revised) This infmation is provided to help you understand the general principles you must apply when marking candidate responses to questions in this Paper. These principles must be read in conjunction with the specific Marking Instructions f each question. (a) (b) Marks f each candidate response must always be assigned in line with these general marking principles and the specific Marking Instructions f the relevant question. Marking should always be positive ie, marks should be awarded f what is crect and not deducted f errs omissions. GENERAL MARKING ADVIE: hemistry igher (Revised) The marking schemes are written to assist in determining the minimal acceptable answer rather than listing every possible crect and increct answer. The following notes are offered to suppt Markers in making judgements on candidates evidence, and apply to marking both end of unit assessments and course assessments. General infmation f markers The general comments given below should be considered during all marking.. There are no half marks awarded. 2. Marks should not be deducted f increct spelling loose language as long as the meaning of the wd(s) is conveyed. Example: Answers like 'distilling' (f 'distillation') and 'it gets hotter' (f 'the temperature rises') should be accepted. 3. A right answer followed by a wrong answer should be treated as a cancelling err and no marks should be given. Example: What colour is seen when blue Fehling s solution is warmed with an aldehyde? The answer 'red, green' gains no marks. 4. If a right answer is followed by additional infmation which does not conflict, the additional infmation should be igned, whether crect not. Example: Why can the tube not be made of copper? If the crect answer is related to a low melting point, 'opper has a low melting point and is coloured grey' would not be treated as having a cancelling err. 5. Full marks are usually awarded f the crect answer to a calculation on its own; the part marks shown in the marking scheme are f use when wking is given. An exception is when candidates are asked to 'Find, by calculation, '. Page 2

4 6. A mark should be deducted f increct missing units only when stated in the marking scheme. No marks should be deducted f increct missing units at intermediate stages in a calculation. 7. As a general rule, where a wrong numerical answer (already penalised) is carried fward to another step, no further penalty is incurred provided the result is used crectly. The exception to this rule is where the marking instructions f a numerical question assign separate concept marks and an arithmetic mark. In such situations, the marking instructions will give clear guidance on the assignment of partial marks. 8. Igne the omission of one atom from a full structural fmula provided the bond is shown. 9. A symbol crect fmula should be accepted in place of a name unless stated otherwise in the marking scheme. 0. When fmulae of ionic compounds are given as answers it will only be necessary to show ion charges if these have been specifically asked f. owever, if ion charges are shown, they must be crect. If increct charges are shown, no marks should be awarded. Page 3

5 . If an answer comes directly from the text of the question, no marks should be given. Example: A student found that 0 05 mol of propane, 3 8 burned to give 82 4 kj of energy. 3 8 (g) (g) 3O 2 (g) O(l) Name the kind of enthalpy change which the student measured. No marks should be given f 'burning' since the wd 'burned' appears in the text. 2. A guiding principle in marking is to give credit f crect chemistry rather than to look f reasons not to give marks. Example : The structure of a hydrocarbon found in petrol is shown below Name the hydrocarbon. Although the punctuation is not crect, '3, methyl-hexane' should gain the full mark. Example 2: A student measured the p of four carboxylic acids to find out how their strength is related to the number of chline atoms in the molecule. The results are shown. ow is the strength of the acids related to the number of chline atoms in the molecule? Although not completely crect, an answer such as 'the me l 2, the stronger the acid' should gain the full mark. 3. Unless the question is clearly about a non-chemistry issue, eg costs in industrial chemistry, a non-chemical answer gains no marks. Example: Why does the (catalytic) converter have a honeycomb structure? A response such as 'to make it wk' may be crect but it is not a chemical answer and the mark should not be given. Page 4

6 Part Two: Marking Instructions f each Question Section A Question Acceptable Answer Question Acceptable Answer B 6 2 D 7 B B 5 D 20 A 6 D 2 A 7 A 22 D D 24 B 0 B 25 A A 26 B 2 27 A 3 D 28 A 4 29 B 5 A 30 D Page 5

7 Question Acceptable Answer/s Max Mark Unacceptable a i K(g) K + (g) + e () K(g) K + (g) + e () Missing increct state symbols a ii Answers can be given either in terms of potassium of chline 3 Answers starting with it are assumed to refer to Potassium Either K has me shells/levels electron further from nucleus diagram showing this () rect and clear use of greater shielding/screening ( clear explanation thereof) () So less energy required to remove electron/ weaker attraction f the electron () l has fewer shells electron closer to nucleus () rect and clear use of less shielding/screening ( clear explanation thereof) () So me energy required to remove electron/stronger attraction f the electron () b 8 ircling O groups but not stating the number Page 6

8 Question Acceptable Answer/s Max Mark Unacceptable 2 a It can react with radicals to fm stable molecules () It can terminate radical (reactions) () It reacts with radicals to stop further radical reactions () It mops-up (free) radicals () It has an unpaired/free electron () Provides electrons (0) 2 b 6 8 O O e (state symbols not required, negative sign on electron not required) Page 7

9 Question Acceptable Answer/s Max Mark Unacceptable 3 a Stating that one (l 3 ) is polar and/ the other (l 4 ) is non-polar () 3 Identifying that l 3 has permanent dipole/permanent dipole attractions and identifying that l 4 has London dispersion fces () Other mark is f a statement linking intermolecular fces/polarity to the solubility in water. Statements such as the following would be acceptable Water is polar () Water has permanent dipole/ permanent dipole attractions () Water is a good solvent f polar molecules () Like dissolves like () 3 b -97 (2) 2 A single mark is available if either of the following operations is crectly executed Either the four relevant values f the bond enthalpies of the, l l, l and l bonds ( multiples thereof) are retrieved from the databook; 243, 44, 326, 428 (igne signs) () the enthalpy values f bond fmation are taken away from the enthalpy values f bond breaking without arithmetic err () (units not required) Page 8

10 Question Acceptable Answer/s Max Mark Unacceptable 4 a i Tollen s acidified dichromate Fehling s Benedict s (please note although Benedict s reagent would not wk in practice, because it appears in igher textbooks, revision guides and the PPA materials f the traditional igher, it can be accepted) (accept other spellings if phonetically crect) 4 a ii arboxylic acid 4 b i It keeps oil & water soluble materials mixed Allow immiscible substances to mix To allow fat and water to mix To fm a suspension to stop it separating (with no mention of water & oil soluble components) to stop layers fming 4 b ii O O O Any structural fmula f glycerol 4 c 6 7 (mg) units not required 2 A single mark is available if either of the following manipulations is crectly executed. rect use of percentage eg mass of chocolate = g = 4 76 g rect use of proption theobromine eg mass of theobromine = 4 a mass Page 9

11 Question Acceptable Answer/s Max Mark Unacceptable 4 d This is an open ended question mark: The student has demonstrated a limited understanding of the chemistry involved. The candidate has made some statement(s) which is/are relevant to the situation, showing that at least a little of the chemistry within the problem is understood. 2 marks: The student has demonstrated a reasonable understanding of the chemistry involved. The student makes some statement(s) which is/are relevant to the situation, showing that the problem is understood. 3 The student has demonstrated no understanding of the chemistry involved. There is no evidence that the student has recognised the area of chemistry involved has given any statement of a relevant chemistry principle. This mark would also be given when the student merely restates the chemistry given in the question. 3 marks: The maximum available mark would be awarded to a student who has demonstrated a good understanding of the chemistry involved. The student shows a good comprehension of the chemistry of the situation and has provided a logically crect answer to the question posed. This type of response might include a statement of the principles involved, a relationship an equation, and the application of these to respond to the problem. This does not mean the answer has to be what might be termed an excellent answer a complete one. Page 0

12 Question Acceptable Answer/s Max Mark Unacceptable 5 a 75 % (2) 2 Total mass of reactants/products = 240 g () Atom Economy = % = 75 % () 240 (Accept 0 75 also, this would be atom economy as a fraction) 5 b 40 % (2) 2 mark is given f either calculating the theetical yield, f wking out the numbers of moles of reactant and product fmed. eg 6 55(g) both and mark is given f calculating the % yield; either using the actual and theetical masses, using the actual number of moles of products and actual number of moles of reactant. %yield = = 52 2 % Page

13 Question Acceptable Answer/s Max Mark Unacceptable 6 a i arboxyl (group) () arboxylic (acid) () 6 a ii 3 N 3 6 a iii O 2 3 Na + O - 2 N 2 3 shtened fmula. harges not required but if shown, both +ve and ve charges must be crect(). ovalent bond shown between Na-O 6 b 25 (minutes) 8.0 to 8.4 (minutes) (units not required. Igne increct units) Page 2

14 Question Acceptable Answer/s Max Mark Unacceptable 6 c Volume = 3 5 cm ml l equivalent (3) 3 One mark is allocated to the crect statement of units of volume. This is the mark in the paper earmarked to reward a candidate s knowledge of chemical units. So volume = (2) One mark is available if either of the following steps is crect alculation of mass of lidocaine eg = 35 (mg) alculation of a volume of solution required eg a mass = a volume 0 6 d i Benzocaine is a smaller/tetracaine is bigger () weaker London Dispersion Fces with Benzocaine () weaker Van der Waal s fces f Benzocaine () Benzocaine has lower b.pt () Benzocaine me soluble/attracted in/ to mobile phase () Benzocaine less strongly attracted to stationary phase () Benzocaine is me polar () Benzocaine takes less time to travel through the apparatus 6 d ii The peaks f lidocaine and caffeine overlap andidate wding f idea of masking The retention times are similar Page 3

15 Question Acceptable Answer/s Max Mark Unacceptable 6 d iii Peak f tetracaine at crect RT with approximately half iginal height Page 4

16 Question Acceptable Answer/s Max Mark Unacceptable 7 a i F successful generation of gas; must have iron sulfide, hydrochlic acid and appropriate glassware to transfer the gas to the gas collection/ measurement apparatus without loss of gas () 2 F the successful collection and measurement of the gas; must have a syringe collect the gas in a measuring cylinder over a nonaqueous liquid () 7 a ii 0 29 (g) (units not required) 3 mark is awarded f a crect strategy to wk out number of moles of hydrogen sulfide (a volume of hydrogen sulfide in whatever unit is shown being divided by a molar volume in whatever unit). mark is awarded f crect strategy to wk out the mass of the iron(ii) sulfide (eg a number of moles of FeS is multiplied by something clearly intended to be the GFM of FeS). mark is awarded f crect arithmetic in both of these steps. (This includes the crect value f the GFM of FeS). This arithmetic mark can only be awarded if both of the concept marks are awarded. 7 b i ovalent molecular discrete covalent 7 b ii Al 2 S O 2Al(O) S rect fmulae f all but one substance, whether balanced not mark 2 Page 5

17 Question Acceptable Answer/s Max Mark Unacceptable 8 a 803, 726, 283 (any two values from this list) () kj mol (f value, no follow through, units not required) () 8 b temperature decrease/keep the same/increase pressure decrease/keep the same/increase 9 a b 4 0 a I 2 + 2e 2I () I 2 + 2e 2I () Igne state symbols Allowing reversible arrows providing the equation is written the crect way round. 0 b i first titre is a rough ( approximate) result/practice first titre is not accurate/not reliable/rogue first titre is too far away from the others you take average of concdant/close results () Page 6

18 Question Acceptable Answer/s Max Mark Unacceptable 0 b ii (mol l units not required) 3 marks 3 Partial marks can be awarded using a scheme of two concept marks, and one arithmetic mark. mark f knowledge of the relationship between moles, concentration and volume. This could be shown by any one of the following steps: alculation of moles thiosulfate(aq) eg = alculation of conc n I 2 eg ( ) 0 02 = Insertion of crect pairings of values f conc n and volume in a valid titration fmula such as V = 2V eg = b b 2 b b 2 mark f knowledge of relationship between moles of S 2 O 3 2 and l 2. This could be shown by any one of the following steps: alculation of moles I 2 from moles S 2 O 2 3 eg /2 = Insertion of crect stoichiometric values in a valid titration fmula such as V 2 V = eg = b b 2 2 mark is awarded f crect arithmetic throughout the calculation. This mark can only be awarded if both concept marks have been awarded. 0 b iii Mass of sodium thiosulfate = 3 96 g () Mention of rinsings () Mention of make up to the mark () 3 Page 7

19 Question Acceptable Answer/s Max Mark Unacceptable a i (anaerobic) fermentation Anaerobic respiration a ii 0 to 0 3 (% abv) b i b ii 3 30 (do not penalise f rounding at intermediate stages) 2 One mark is available if the candidate has either arried out a calculation to take into account the dilution of the whisky e.g. used a scaling 46 fact of 65 as crectly calculated the cost f a given volume of alcohol by use of the e.g. used the scaling fact of 300/95 b iii 5-butyl-4-ethyltetrahydrofuran-2-ol 4-ethyl-5-butyltetrahydrofuran-2-ol c i addition hydration c ii no change Page 8

20 Question Acceptable Answer/s Max Mark Unacceptable 2 This is an open ended question mark: The student has demonstrated a limited understanding of the chemistry involved. The candidate has made some statement(s) which is/are relevant to the situation, showing that at least a little of the chemistry within the problem is understood. 2 marks: The student has demonstrated a reasonable understanding of the chemistry involved. The student makes some statement(s) which is/are relevant to the situation, showing that the problem is understood. 3 The student has demonstrated no understanding of the chemistry involved. There is no evidence that the student has recognised the area of chemistry involved has given any statement of a relevant chemistry principle. This mark would also be given when the student merely restates the chemistry given in the question. 3 marks: The maximum available mark would be awarded to a student who has demonstrated a good understanding of the chemistry involved. The student shows a good comprehension of the chemistry of the situation and has provided a logically crect answer to the question posed. This type of response might include a statement of the principles involved, a relationship an equation, and the application of these to respond to the problem. This does not mean the answer has to be what might be termed an excellent answer a complete one. Page 9

21 Question Acceptable Answer/s Max Mark Unacceptable 3 a Structures with missing -atoms Any structure with a methyl group in the equatial position. equivalent,3-dimethylcyclohexane structure with both methyl groups in axial positions 3 b i The bigger the group the greater the strain The larger the (halogen) atom the greater the strain The me atoms in a group, the greater the strain Any other statement which is consistent with the values presented Increct reference to a group as a molecule 3 b ii 7 6 (kj mol ) (Units not required, igne increct units) [END OF MARKING INSTRUTIONS] Page 20

22 SETION A Read carefully heck that the answer sheet provided is f hemistry igher (Revised) (Section A). 2 F this section of the examination you must use an B pencil and, where necessary, an eraser. 3 heck that the answer sheet you have been given has your name, date of birth, SN (Scottish andidate Number) and entre Name printed on it. Do not change any of these details. 4 If any of this infmation is wrong, tell the Invigilat immediately. 5 If this infmation is crect, print your name and seat number in the boxes provided. 6 The answer to each question is either A, B, D. Decide what your answer is, then, using your pencil, put a hizontal line in the space provided (see sample question below). 7 There is only one crect answer to each question. 8 Any rough wking should be done on the question paper the rough wking sheet, not on your answer sheet. 9 At the end of the examination, put the answer sheet f Section A inside the front cover of your answer book. Sample Question To show that the ink in a ball-pen consists of a mixture of dyes, the method of separation would be A chromatography B fractional distillation fractional crystallisation D filtration. The crect answer is A chromatography. The answer A has been clearly marked in pencil with a hizontal line (see below). A B D hanging an answer If you decide to change your answer, carefully erase your first answer and using your pencil, fill in the answer you want. The answer below has been changed to D. A B D [X273/2/02] Page two

23 . Which of the following elements has the greatest attraction f bonding electrons? A B D Lithium hline Sodium Bromine 5. The diagram shows the melting points of successive elements across a period in the Periodic Table. 2. Which of the following elements exists as discrete molecules? A B D Bon arbon (diamond) Silicon Sulfur Melting point / Y 3. Which of the following statements is true? A B D The potassium ion is larger than the potassium atom. The chlide ion is smaller than the chline atom. The sodium atom is larger than the sodium ion. The oxygen atom is larger than the oxide ion. 4. Which type of bonding is never found in elements? A B D Metallic London dispersion fces Polar covalent Non-polar covalent Group number Which of the following is a crect reason f the low melting point of element Y? A B D It has weak ionic bonds. It has weak covalent bonds. It has weakly-held outer electrons. It has weak fces between molecules. [Turn over [X273/2/02] Page three

24 6. The structures f molecules of four liquids are shown below. Which liquid will be the most viscous? 8. O A O Which of the following compounds is an isomer of the structure shown above? A B Butanal Butanone B D Butan--ol Butanoic acid O 9. A compound with molecular fmula 6 2 O 2, could be A B D hexanal hexan-2-ol hexan-2-one hexanoic acid. O 0. An ester has the following structural fmula D O O 7. Which of the following elements is the strongest reducing agent? A B D Lithium Bromine Fluine Aluminium OO 2 3 The name of this ester is A B D propyl propanoate ethyl butanoate butyl ethanoate ethyl propanoate.. Esters are fmed by the reaction between which two functional groups? A B D A hydroxyl group and a carboxyl group A hydroxyl group and a carbonyl group A hydroxide group and a carboxyl group A hydroxide group and a carbonyl group 2. Oils are generally A B D solid at room temperature and contain a high proption of unsaturated molecules solid at room temperature and contain a high proption of saturated molecules liquid at room temperature and contain a high proption of unsaturated molecules liquid at room temperature and contain a high proption of saturated molecules. [X273/2/02] Page four

25 3. A tripeptide X has the structure 2 N 3 ( 3 ) 2 ON 2 ON OO Partial hydrolysis of X yields a mixture of dipeptides. Which of the following dipeptides could be produced on hydrolysing X? 4. Erythrose can be used in the production of a chewing gum that helps prevent tooth decay. O O O 2 Which of the following compounds will be the best solvent f erythrose? O A 3 A N 2 ON OO B 3 ( 3 ) N ON OO B ( 3 ) O 2 N ON 2 OO D D 2 N 2 ON ( 3 ) 2 OO l l l 5. When a protein is denatured A B its overall shape is distted its amide links are hydrolysed it is broken into separate peptide fragments D it decomposes into amino acids. [Turn over [X273/2/02] Page five

26 6. Which two isomers would each produce an acid when warmed with acidified potassium dichromate solution? O Which of the following ganic compounds is an isomer of hexanal? A B D 2-Methylbutanal 3-Methylpentan-2-one 2,2-Dimethylbutan--ol 3-Ethylpentanal O O O A and 2 B 2 and 3 and 4 D 3 and 4 8. Soaps are produced by the following reaction. O O 7 35 O O _ O NaO(aq) O + 3 OO Na O O 7 35 O This reaction is an example of A B D condensation esterification hydrolysis oxidation. [X273/2/02] Page six

27 9. Limonene is one of the terpene molecules responsible f the flavour of lemons ow many isoprene units are used in the production of one limonene molecule? A B 2 3 D A mixture of magnesium bromide and magnesium sulfate is known to contain 3 mol of magnesium and 4 mol of bromide ions. ow many moles of sulfate ions are present? A B 2 3 D (g) + 5O 2 (g) 4O 2 (g) O(l) ethyne What volume of gas would be produced by the complete combustion of 00 cm 3 of ethyne gas? All volumes were measured at atmospheric pressure and room temperature. A 200 cm 3 B 300 cm cm 3 D 800 cm SO 2 (g) + O 2 (g) 2SO 3 (g) The equation represents a mixture at equilibrium. Which line in the table is true f the mixture after a further 2 hours of reaction? Rate of fward reaction Rate of back reaction A decreases decreases B increases increases unchanged decreases D unchanged unchanged 23. In which of the following would an increase in pressure result in the equilibrium position being moved to the left? A N 2 (g) (g) 2N 3 (g) B O(g) + 2 O(g) O 2 (g) + 2 (g) 4 (g) + 2 O(g) O(g) (g) D Fe 2 O 3 (s) + 3O(g) 2Fe(s) + 3O 2 (g) 24. Ammonia is made by the aber Process. N 2 (g) (g) 2N 3 (g) The equilibrium position lies to the left. Which line in the table is crect? Atom Economy Percentage Yield A high high B high low low high D low low [Turn over [X273/2/02] Page seven

28 25. In which of the following will both changes result in an increase in the rate of a chemical reaction? A B D A decrease in activation energy and an increase in the frequency of collisions. An increase in activation energy and a decrease in particle size. An increase in temperature and an increase in the particle size. An increase in concentration and a decrease in the surface area of the reactant particles. 26. Which of the following diagrams represents an exothermic reaction which is most likely to take place at room temperature? A Potential energy Reaction pathway B Potential energy Reaction pathway Potential energy Reaction pathway D Potential energy Reaction pathway [X273/2/02] Page eight

29 27. The enthalpy of combustion of methanol is 727 kj mol. 28. What mass of methanol has to be burned to produce 72 7 kj? A B D 3 2 g 32 0 g 72 7 g g (s) + 2 (g) + O 2 (g) OO(l) = a OO(l) + ½O 2 (g) O 2 (g) + 2 O(l) = b (s) + O 2 (g) O 2 (g) 2 (g) + ½O 2 (g) 2 O(l) = c = d What is the relationship between a, b, c and d? A B D a = c + d b a = b c d a = b c d a = c + b + d cm 3 of a solution could be most accurately measured out using a A B D 50 cm 3 beaker 50 cm 3 burette 50 cm 3 pipette 50 cm 3 measuring cylinder. 30. Aluminium carbonate can be produced by the following reaction. 2All 3 (aq) + 3K 2 O 3 (aq) Al 2 (O 3 ) 3 (s) + 6Kl(aq) The most suitable method f obtaining a sample of the aluminium carbonate is A B D collection over water distillation evapation filtration. andidates are reminded that the answer sheet MUST be returned INSIDE the front cover of this answer book. [Turn over [X273/2/02] Page nine

30 [BLANK PAGE] [X273/2/02] Page ten

31 SETION B All answers must be written clearly and legibly in ink. Marks DO NOT WRITE IN TIS MARGIN. Attempts have been made to make foods healthier by using alternatives to traditional cooking ingredients. (a) An alternative to common salt contains potassium ions and chlide ions. (i) Write an ion-electron equation f the first ionisation energy of potassium. (ii) Explain clearly why the first ionisation energy of potassium is smaller than that of chline. (b) A calie-free replacement f fat can be made by reacting fatty acids with the hydroxyl groups on a molecule of sucrose. A structural fmula f sucrose is shown. 3 O O 2 O O O 2 O O O O O 2 O ow many fatty acid molecules can react with one molecule of sucrose? (5) [X273/2/02] Page eleven [Turn over

32 2. Suncreams contain antioxidants. Marks DO NOT WRITE IN TIS MARGIN (a) The antioxidant, compound A, can prevent damage to skin by reacting with free radicals such as NO O O N O O 3 O 3 3 O N O 3 ompound A O Why can compound A be described as a free radical scavenger in the reaction shown above? (b) Another antioxidant used in skin care products is vitamin, 6 8 O 6. omplete the ion-electron equation f the oxidation of vitamin. 6 8 O 6 (aq) 6 6 O 6 (aq) (2) [X273/2/02] Page twelve

33 3. The structures below show molecules that contain chline atoms. Marks DO NOT WRITE IN TIS MARGIN l l l trichlomethane l l l l tetrachlomethane (a) The compounds shown above are not very soluble in water. Trichlomethane is around ten times me soluble in water than tetrachlomethane. Explain clearly why trichlomethane is me soluble in water than tetrachlomethane. Your answer should include the names of the intermolecular fces involved. 3 (b) hlomethane can be produced by the reaction of methane with chline. 4 (g) + l 2 (g) 3 l(g) + l(g) Using bond enthalpies from the data booklet, calculate the enthalpy change, in kj mol, f this reaction. 2 (5) [X273/2/02] Page thirteen [Turn over

34 4. hocolate contains various compounds. Marks DO NOT WRITE IN TIS MARGIN (a) Many of the flavour and aroma molecules found in chocolate are aldehydes and ketones. Two examples are shown below. O O phenylethanal,3-diphenylpropan-2-one Phenylethanal can be easily oxidised but,3-diphenylpropan-2-one cannot. (i) Name a chemical that could be used to distinguish between these two compounds. (ii) Name the type of ganic compound fmed when phenylethanal is oxidised. (b) Glycerol monostearate is an emulsifier used in chocolate O O O O (i) Why is glycerol monostearate added to chocolate? (ii) Draw a structural fmula f glycerol. [X273/2/02] Page fourteen

35 4. (continued) Marks DO NOT WRITE IN TIS MARGIN (c) Theobromine, a compound present in chocolate, can cause illness in dogs and cats. To decide if treatment is necessary, vets must calculate the mass of theobromine consumed. 0 g of chocolate contains 4 mg of theobromine. alculate the mass, in mg, of theobromine in a 7 g biscuit of which 28% is chocolate. Show your wking clearly. 2 (d) The flavour and texture of chocolate comes from a blend of compounds. Using your knowledge of chemistry, describe how you could show that there are ionic compounds and covalent compounds present in chocolate. [X273/2/02] Page fifteen [Turn over 3 (9)

36 5. Aspirin, a common pain-killer, can be made by the reaction of salicylic acid with ethanoic anhydride. Marks DO NOT WRITE IN TIS MARGIN O O O O O O O O O O O O 7 6 O O O O 2 salicylic acid ethanoic anhydride aspirin ethanoic acid mass of one mole = 38 g mass of one mole = 02 g mass of one mole = 80 g mass of one mole = 60 g (a) alculate the atom economy f the fmation of aspirin using this method. Show your wking clearly. 2 (b) In a labaty preparation of aspirin, 5 02 g of salicylic acid produced 2 62 g of aspirin. alculate the percentage yield of aspirin. Show your wking clearly. 2 (4) [X273/2/02] Page sixteen

37 6. Dental anaesthetics are substances used to reduce discomft during treatment. Marks DO NOT WRITE IN TIS MARGIN (a) Lidocaine is a dental anaesthetic. 3 N O 2 2 N Lidocaine causes numbness when applied to the gums. This effect wears off as the lidocaine is hydrolysed. One of the products of the hydrolysis of lidocaine is compound. O O 2 2 N compound (i) Name the functional group circled above. (ii) Draw a structural fmula f the other compound produced when lidocaine is hydrolysed. (iii) Draw a structural fmula f the ganic compound fmed when compound reacts with NaO(aq). [X273/2/02] Page seventeen [Turn over

38 6. (continued) Marks DO NOT WRITE IN TIS MARGIN (b) The table below shows the duration of numbness f common anaesthetics. Name of anaesthetic Structure Duration of numbness/ minutes O procaine 2 N 2 O 2 2 N lidocaine 3 N O 2 2 N mepivacaine 3 N O N anaesthetic X 2 N O O 2 3 N Estimate the duration of numbness, in minutes, f anaesthetic X. [X273/2/02] Page eighteen

39 6. (continued) Marks DO NOT WRITE IN TIS MARGIN (c) The maximum safe dose of lidocaine f an adult is 4 5 mg of lidocaine per kg of body mass. 0 cm 3 of lidocaine solution contains 0 mg of lidocaine. alculate the maximum volume of lidocaine solution that could be given to a 70 kg adult. Show your wking clearly. 3 [Turn over [X273/2/02] Page nineteen

40 6. (continued) Marks DO NOT WRITE IN TIS MARGIN (d) When fensic scientists analyse illegal drugs, anaesthetics such as lidocaine are sometimes found to be present. The gas chromatogram below is from an illegal drug. A B D E A benzocaine B lidocaine caffeine D cocaine E tetracaine Retention time / minutes (i) The structures of benzocaine and tetracaine are shown below. N O 2 3 benzocaine O N N 3 tetracaine 3 Suggest why benzocaine has a shter retention time than tetracaine. [X273/2/02] Page twenty

41 6. (d) (continued) (ii) Why is it difficult to obtain accurate values f the amount of lidocaine present in a sample containing large amounts of caffeine? Marks DO NOT WRITE IN TIS MARGIN (iii) Add a peak to the diagram below to complete the chromatogram f a second sample that only contains half the amount of tetracaine compared to the first Retention time / minutes (0) [Turn over [X273/2/02] Page twenty-one

42 7. ydrogen sulfide is a toxic gas with the smell of rotten eggs. Marks DO NOT WRITE IN TIS MARGIN (a) ydrogen sulfide gas can be prepared by the reaction of iron(ii) sulfide with excess dilute hydrochlic acid: FeS(s) + 2l(aq) Fel 2 (aq) + 2 S(g) (i) ydrogen sulfide gas is very soluble in water. Draw a diagram to show an assembled apparatus that could be used to measure the volume of 2 S gas produced when a sample of iron(ii) sulfide reacts with hydrochlic acid. Your diagram should be labelled and should show the names of any chemicals used. 2 (ii) alculate the mass, in g, of iron(ii) sulfide required to produce 79 cm 3 of hydrogen sulfide gas. (Take the molar volume of hydrogen sulfide to be 24 litres mol.) Show your wking clearly. 3 [X273/2/02] Page twenty-two

43 7. (continued) Marks DO NOT WRITE IN TIS MARGIN (b) ydrogen sulfide gas produced from iron(ii) sulfide is often contaminated with hydrogen gas and gaseous arsenic compounds. (i) Arsenic(III) sulfide is an ange-yellow powder which is insoluble in water. Below 30 it can sublime, turning from a solid to a gas. Name the type of bonding and structure present in arsenic(iii) sulfide. (ii) To avoid these contaminants, hydrogen sulfide can be made by reacting aluminium sulfide with water. ydrogen sulfide and aluminium hydroxide are produced. Write a balanced equation f the production of hydrogen sulfide from aluminium sulfide and water. 2 (8) [Turn over [X273/2/02] Page twenty-three

44 8. Mobile phones are being developed that can be powered by methanol. Methanol can be made by a two-stage process. Marks DO NOT WRITE IN TIS MARGIN (a) In the first stage, methane is reacted with steam to produce a mixture of carbon monoxide and hydrogen. 4 (g) + 2 O(g) O(g) (g) Use the data below to calculate the enthalpy change, in kj mol, f the fward reaction. O(g) + ½O 2 (g) O 2 (g) = 283 kj mol 2 (g) + ½O 2 (g) 2 O(g) = 242 kj mol 4 (g) + 2O 2 (g) O 2 (g) O(g) = 803 kj mol Show your wking clearly. 2 (b) In the second stage, the carbon monoxide and hydrogen react to produce methanol. O(g) (g) 3 O(g) = 9 kj mol ircle the crect wds in the table to show the changes to temperature and pressure that would favour the production of methanol. (An additional table, if required, can be found on Page thirty-four.) temperature pressure decrease / keep the same / increase decrease / keep the same / increase (3) [X273/2/02] Page twenty-four

45 9. Dark blue compounds can be made by reacting ammonia with copper ions. To determine the number of ammonia molecules that react with each copper ion, a student prepared the following mixtures and measured their colour intensity. Marks DO NOT WRITE IN TIS MARGIN Mixture A B D E F Volume of 0 mol l u 2+ solution, cm Volume of 0 mol l N 3 solution, cm olour intensity (An additional table, if required, can be found on Page thirty-four.) (a) omplete the table to show the volume of N 3 solution required f the final experiment. (b) The number of ammonia molecules that react with each copper ion can be found from the mixture with the greatest colour intensity. ow many ammonia molecules react with each copper ion? (2) [Turn over [X273/2/02] Page twenty-five

46 0. Solutions containing iodine are used to treat foot rot in sheep. The concentration of iodine in a solution can be determined by titrating with a solution of thiosulfate ions. Marks DO NOT WRITE IN TIS MARGIN I 2 + 2S 2 O 3 2 thiosulfate ions 2I + S 4 O 6 2 (a) Write an ion-electron equation f the reaction of the oxidising agent in the titration. (b) Three 20 0 cm 3 samples of a sheep treatment solution were titrated with 0 0 mol l thiosulfate solution. The results are shown below. Sample Volume of thiosulfate/cm (i) Why is the volume of sodium thiosulfate used in the calculation taken to be 8 5 cm 3, although this is not the average of the three titres in the table? [X273/2/02] Page twenty-six

47 0. (b) (continued) (ii) alculate the concentration of iodine, in mol l, in the foot rot treatment solution. Show your wking clearly. Marks DO NOT WRITE IN TIS MARGIN 3 (iii) Describe how to prepare 250 cm 3 of a 0 0 mol l standard solution of sodium thiosulfate, Na 2 S 2 O 3. Your answer should include the mass, in g, of sodium thiosulfate required. 3 (8) [X273/2/02] Page twenty-seven [Turn over

48 . Ethanol has many uses. Marks DO NOT WRITE IN TIS MARGIN (a) Ethanol is found at relatively low concentrations in wine. (i) Name the chemical reaction that produces ethanol in wine. (ii) Standard ethanol solutions were used to produce a graph of density against concentration of ethanol, given as a percentage of alcohol by volume (% abv) Density/g cm oncentration of ethanol / % abv What is the concentration of ethanol, in units of % abv, in a solution of density g cm 3? [X273/2/02] Page twenty-eight

49 . (continued) Marks DO NOT WRITE IN TIS MARGIN (b) Whisky contains a higher concentration of ethanol. (i) Befe 980, the concentration of alcohol in drinks was measured in terms of degrees proof. The concentration of alcohol in two drinks is shown in the table below, both as % abv and degrees proof. Sample Alcohol concentration / % abv Alcohol concentration / degrees proof Wine Sherry A cask strength whisky has an alcohol concentration of 65% abv. alculate the alcohol concentration of this whisky in degrees proof. (ii) A barrel containing 95 litres of cask strength whisky costs 300. The cask strength whisky is diluted with water to reduce the concentration of alcohol from 65% abv to 46% abv befe it is bottled. alculate the cost of the cask strength whisky needed to produce a 0 70 litre bottle. Show your wking clearly. 2 [X273/2/02] Page twenty-nine [Turn over

50 . (b) (continued) (iii) 5-Butyl-4-methyltetrahydrofuran-2-ol is a flavour compound found in whisky sted in oak barrels. Marks DO NOT WRITE IN TIS MARGIN 3 O 2 O butyl-4-methyltetrahydrofuran-2-ol Write the systematic name f the compound shown below. O 2 O (c) Ethanol, f use in industrial processes, can be produced by reacting ethene gas with steam. 2 4 (g) + 2 O(g) 2 5 O(g) (i) What name is given to this type of chemical reaction? (ii) What would happen to the equilibrium position if a catalyst was used? (8) [X273/2/02] Page thirty

51 2. ooking involves many chemical reactions. Proteins, fats, oils and esters are some examples of compounds found in food. A chemist suggested that cooking food could change compounds from being fat-soluble to water-soluble. Use your knowledge of chemistry to comment on the accuracy of this statement. Marks DO NOT WRITE IN TIS MARGIN (3) [Turn over [X273/2/02] Page thirty-one

52 3. ycloalkanes are found in nature. A representation of cyclohexane is shown below. Marks DO NOT WRITE IN TIS MARGIN The six hydrogen atoms marked in bold are said to be in axial positions. In the molecule of,2-dimethylcyclohexane shown below, two methyl groups are in axial positions. 3 3 (a) omplete the structure shown below to show a molecule of,3-dimethylcyclohexane in which both the methyl groups are in axial positions. (An additional diagram, if required, can be found on Page thirty-four.) [X273/2/02] Page thirty-two

53 3. (continued) Marks DO NOT WRITE IN TIS MARGIN (b) Axial groups on the same side of a cyclohexane ring can repel each other. The strength of the repulsion is known as the steric strain. The table below shows values which allow the steric strain to be calculated. Axial groups Steric strain /kj mol and 0 0 and F 0 5 and Br 0 and and ( 3 ) 3 4 F example: F Steric strain = = 2 (Steric strain between and F) = 0 kj mol (i) Write a general statement, linking the size of the steric strain to the type of axial group present. (ii) alculate, in kj mol, the steric strain f the molecule shown below. 3 Steric strain = (3) [END OF QUESTION PAPER] [X273/2/02] Page thirty-three

54 DO NOT WRITE IN TIS MARGIN ADDITIONAL TABLE FOR USE IN QUESTION 8(b) temperature pressure decrease / keep the same / increase decrease / keep the same / increase ADDITIONAL TABLE FOR USE IN QUESTION 9(a) Mixture A B D E F Volume of 0 mol l u 2+ solution, cm Volume of 0 mol l N 3 solution, cm olour intensity ADDITIONAL DIAGRAM FOR USE IN QUESTION 3(a) [X273/2/02] Page thirty-four

55 DO NOT WRITE IN TIS MARGIN ADDITIONAL SPAE FOR ANSWERS [X273/2/02] Page thirty-five

56 [BLANK PAGE]

57 203 hemistry igher (Revised) Finalised Marking Instructions Scottish Qualifications Authity 203 The infmation in this publication may be reproduced to suppt SQA qualifications only on a non-commercial basis. If it is to be used f any other purposes written permission must be obtained from SQA s NQ Assessment team. Where the publication includes materials from sources other than SQA (secondary copyright), this material should only be reproduced f the purposes of examination assessment. If it needs to be reproduced f any other purpose it is the centre s responsibility to obtain the necessary copyright clearance. SQA s NQ Assessment team may be able to direct you to the secondary sources. These Marking Instructions have been prepared by Examination Teams f use by SQA Appointed Markers when marking External ourse Assessments. This publication must not be reproduced f commercial trade purposes.

58 Part One: General Marking Principles f hemistry igher (Revised) This infmation is provided to help you understand the general principles you must apply when marking candidate responses to questions in this Paper. These principles must be read in conjunction with the specific Marking Instructions f each question. (a) (b) Marks f each candidate response must always be assigned in line with these general marking principles and the specific Marking Instructions f the relevant question. Marking should always be positive ie, marks should be awarded f what is crect and not deducted f errs omissions. GENERAL MARKING ADVIE: hemistry igher (Revised) The marking schemes are written to assist in determining the minimal acceptable answer rather than listing every possible crect and increct answer. The following notes are offered to suppt Markers in making judgements on candidates evidence, and apply to marking both end of unit assessments and course assessments. General infmation f markers The general comments given below should be considered during all marking.. There are no half marks awarded. 2. Marks should not be deducted f increct spelling loose language as long as the meaning of the wd(s) is conveyed. Example: Answers like 'distilling' (f 'distillation') and 'it gets hotter' (f 'the temperature rises') should be accepted. 3. A right answer followed by a wrong answer should be treated as a cancelling err and no marks should be given. Example: What colour is seen when blue Fehling s solution is warmed with an aldehyde? The answer 'red, green' gains no marks. 4. If a right answer is followed by additional infmation which does not conflict, the additional infmation should be igned, whether crect not. Example: Why can the tube not be made of copper? If the crect answer is related to a low melting point, 'opper has a low melting point and is coloured grey' would not be treated as having a cancelling err. 5. Full marks are usually awarded f the crect answer to a calculation on its own; the part marks shown in the marking scheme are f use when wking is given. An exception is when candidates are asked to 'Find, by calculation, '. Page 2

59 6. A mark should be deducted f increct missing units only when stated in the marking scheme. No marks should be deducted f increct missing units at intermediate stages in a calculation. 7. As a general rule, where a wrong numerical answer (already penalised) is carried fward to another step, no further penalty is incurred provided the result is used crectly. The exception to this rule is where the marking instructions f a numerical question assign separate concept marks and an arithmetic mark. In such situations, the marking instructions will give clear guidance on the assignment of partial marks. 8. Igne the omission of one atom from a full structural fmula provided the bond is shown. 9. A symbol crect fmula should be accepted in place of a name unless stated otherwise in the marking scheme. 0. When fmulae of ionic compounds are given as answers it will only be necessary to show ion charges if these have been specifically asked f. owever, if ion charges are shown, they must be crect. If increct charges are shown, no marks should be awarded. Page 3

60 . If an answer comes directly from the text of the question, no marks should be given. Example: A student found that 0 05 mol of propane, 3 8 burned to give 82 4 kj of energy. 3 8 (g) (g) 3O 2 (g) O(l) Name the kind of enthalpy change which the student measured. No marks should be given f 'burning' since the wd 'burned' appears in the text. 2. A guiding principle in marking is to give credit f crect chemistry rather than to look f reasons not to give marks. Example : The structure of a hydrocarbon found in petrol is shown below Name the hydrocarbon. Although the punctuation is not crect, '3, methyl-hexane' should gain the full mark. Example 2: A student measured the p of four carboxylic acids to find out how their strength is related to the number of chline atoms in the molecule. The results are shown. ow is the strength of the acids related to the number of chline atoms in the molecule? Although not completely crect, an answer such as 'the me l 2, the stronger the acid' should gain the full mark. 3. Unless the question is clearly about a non-chemistry issue, eg costs in industrial chemistry, a non-chemical answer gains no marks. Example: Why does the (catalytic) converter have a honeycomb structure? A response such as 'to make it wk' may be crect but it is not a chemical answer and the mark should not be given. Page 4

61 Part Two: Marking Instructions f each Question Section A Question Acceptable Answer Question Acceptable Answer B 6 2 D 7 B B 5 D 20 A 6 D 2 A 7 A 22 D D 24 B 0 B 25 A A 26 B 2 27 A 3 D 28 A 4 29 B 5 A 30 D Page 5

62 Question Acceptable Answer/s Max Mark Unacceptable a i K(g) K + (g) + e () K(g) K + (g) + e () Missing increct state symbols a ii Answers can be given either in terms of potassium of chline 3 Answers starting with it are assumed to refer to Potassium Either K has me shells/levels electron further from nucleus diagram showing this () rect and clear use of greater shielding/screening ( clear explanation thereof) () So less energy required to remove electron/ weaker attraction f the electron () l has fewer shells electron closer to nucleus () rect and clear use of less shielding/screening ( clear explanation thereof) () So me energy required to remove electron/stronger attraction f the electron () b 8 ircling O groups but not stating the number Page 6

63 Question Acceptable Answer/s Max Mark Unacceptable 2 a It can react with radicals to fm stable molecules () It can terminate radical (reactions) () It reacts with radicals to stop further radical reactions () It mops-up (free) radicals () It has an unpaired/free electron () Provides electrons (0) 2 b 6 8 O O e (state symbols not required, negative sign on electron not required) Page 7

64 Question Acceptable Answer/s Max Mark Unacceptable 3 a Stating that one (l 3 ) is polar and/ the other (l 4 ) is non-polar () 3 Identifying that l 3 has permanent dipole/permanent dipole attractions and identifying that l 4 has London dispersion fces () Other mark is f a statement linking intermolecular fces/polarity to the solubility in water. Statements such as the following would be acceptable Water is polar () Water has permanent dipole/ permanent dipole attractions () Water is a good solvent f polar molecules () Like dissolves like () 3 b -97 (2) 2 A single mark is available if either of the following operations is crectly executed Either the four relevant values f the bond enthalpies of the, l l, l and l bonds ( multiples thereof) are retrieved from the databook; 243, 44, 326, 428 (igne signs) () the enthalpy values f bond fmation are taken away from the enthalpy values f bond breaking without arithmetic err () (units not required) Page 8

65 Question Acceptable Answer/s Max Mark Unacceptable 4 a i Tollen s acidified dichromate Fehling s Benedict s (please note although Benedict s reagent would not wk in practice, because it appears in igher textbooks, revision guides and the PPA materials f the traditional igher, it can be accepted) (accept other spellings if phonetically crect) 4 a ii arboxylic acid 4 b i It keeps oil & water soluble materials mixed Allow immiscible substances to mix To allow fat and water to mix To fm a suspension to stop it separating (with no mention of water & oil soluble components) to stop layers fming 4 b ii O O O Any structural fmula f glycerol 4 c 6 7 (mg) units not required 2 A single mark is available if either of the following manipulations is crectly executed. rect use of percentage eg mass of chocolate = g = 4 76 g rect use of proption theobromine eg mass of theobromine = 4 a mass Page 9