2003 Chemistry. Higher. Finalised Marking Instructions

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Reynold Cunningham
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1 2003 Chemistry Higher Finalised Marking Instructions

2 Higher Chemistry General infmation f markers The general comments given below should be considered during all marking. 1 Marks should not be deducted f increct spelling loose language as long as the meaning of the wd(s) is conveyed. Example: Answers like 'distiling' (f 'distillation') and 'it gets hotter' (f 'the temperature rises') should be accepted. 2 A right answer followed by a wrong answer should be treated as a cancelling err and no marks should be given. Example: What is the colour of universal indicat in acid solution? The answer 'red, blue' gains no marks. 3 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, 'It has a low melting point and is coloured grey' would not be treated as having a cancelling err. 4 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,... 5 A half mark should be deducted in a calculation f each arithmetic slip. 6 A half 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 Where a wrong numerical answer (already penalised) is carried fward to another step, no further penalty is incurred provided the result is used crectly. 8 Igne the omission of one H atom from a full structural fmula provided the bond is shown. 9 With structures involving an OH an NH 2 group, a half mark should be deducted if the 'O' 'N' are not bonded to a carbon, i.e. OH CH 2 and NH 2 CH When drawing structural fmulae, a half mark should be deducted if the bond points to the 'wrong' atom, eg C C OH 11 A symbol crect fmula should be accepted in place of a name unless stated otherwise in the marking scheme. 12 When fmulae of ionic compounds are given as answers it will only be necessary to show ion charges if these has been specifically asked f. However, if ion charges are shown, they must be crect. If increct charges are shown, no marks should be awarded. Page 2

3 13 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, C 3 H 8 burned to give 82 4 kj of energy. C 3 H 8 (g) + 5O 2 (g) 3CO 2 (g) + 4H 2 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. 14 A guiding principle in marking is to give credit f (partially) crect chemistry rather than to look f reasons not to give marks. Example 1: The structure of a hydrocarbon found in petrol is shown below. CH 3 CH 3 CH 2 CH CH 2 CH 2 CH 3 Name the hydrocarbon. mark. Although the punctuation is not crect, '3, methyl-hexane' should gain the full Example 2: A student measured the ph 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. Structural fmula ph CH 3 COOH 1 65 CH 2 ClCOOH 1 27 CHCl 2 COOH 0 90 CCl 3 COOH 0 51 How 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 Cl 2, the stronger the acid' should gain the full mark. 15 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. 16 When it is very difficult to make a decision about a partially crect answer, a half mark can be awarded. 17 When marks have been totalled, a half mark should be rounded up. Page 3

4 2003 Chemistry Higher Marking Scheme Section A 1. C 11. D 21. A 31. D 2. D 12. A 22. C 32. B 3. B 13. B 23. D 33. A 4. C 14. D 24. D 34. D 5. D 15. C 25. A 35. B 6. B 16. C 26. D 36. D 7. C 17. A 27. C 37. C 8. B 18. C 28. A 38. C 9. C 19. A 29. B 39. A 10. D 20. B 30. A 40. B Page 4

5 Mark Scheme Wth ½ Wth 0 1. (a) 2,3,3 trimethylpentane 3,3,2 trimethlypentane (commas, dash may be omitted) 1 2-methyl, 3-dimethylpentane 3,3,4 trimethylpentane 2,3,3 methylpentane 2,3 methylpentane methylpentane (b) cycloalkanes aromatics (benzenes) benzyl hydrocarbons 1 ring structure naphtha cyclic phenol (2) Page 5

6 Mark Scheme Wth ½ Wth 0 2. (a) Strong rigid durable tough hard hard to puncture 1 light does not burn (b) amide link peptide link 1 polyamide polypeptide amino group amine group (2) Page 6

7 Mark Scheme Wth ½ Wth 0 3. (a) plotting points crectly and joining with a line 1 points not joined one point not plotted crectly points joined by straight line (b) 210 Po 206 Pb + He ( α) numbers on rhs any wrong subscript superscript 210 α Po 206 Pb 1 (c) 210 g contain 6 x (atoms) 6 x in 1 mol 105 g contain ½ x 6 x (atoms) = 3 x (3) Page 7

8 Mark Scheme Wth ½ Wth 0 4. (a) any suggestion that iron fmed is molten in liquid state answer implies that iron flows down into crack 1 rail melts, etc iron is fmed (in question) exothermic (b) H required = H1 H2 = (-1676) (-825) = kj (mol -1 ) (2) Page 8

9 Mark Scheme Wth ½ Wth 0 5. (a) synthesis gas syn. gas 1 synthetic gas (b) oxidation dehydrogenation 1 (c) (i) O H H O O N C N H2N C NH2 NH2 C H H 1 H NCON H H H (ii) thermosetting 1 thermohardening (4) Page 9 NH2

10 Mark Scheme Wth ½ Wth 0 6. (a) (i) reactants products could go on fire (flammable) to prevent burning 1 (ii) to condense any vapours ( reactants products which evapate) 1 easier to control the temperature/condensation safer way to heat (b) H H O H H H H H C C O C C C C C H H H H H H H O CH3CH2-O-CCH2CH2CH2CH3 1 Page 10

11 Mark Scheme Wth ½ Wth 0 6. (c) 1 mol C2H5OH = 46 g g x 130 g g 70 x 130 x g 46 = 7.12 g 1 mol C2H5OH = 46 g 46 g 130 g g 130 x = g 46 actual yield = x = 7.12 g (-½ f wrong no units) (5) Page 11

12 Mark Scheme Wth ½ Wth 0 7. (a) 4.0 moles of Mg = = mol x 50 moles of acid = = 0.2 moles 1000 mole ratio = 1 mol Mg : 2 mol acid Not enough HCl(aq). Therefe Mg in excess (1) 2 (b) to syringe System not sealed water 1 (c) rate slower volume same 1 (4) Page 12

13 Mark Scheme Wth ½ Wth 0 8. (a) (i) carbonyl group at end of carbon chain in aldehyde only one H attached to carbonyl aldehyde C O ( CHO) H ketone O C C C ( C C O C ) 1 (ii) blue ange/brick red/brown 1 (iii) C3H6O + H2O 2H + (aq) + C2H5COOH + 2e - 1 H + (aq) and e - on rhs but not balanced (iv) propanoic (acid) 1 (b) (i) addition reduction 1 (ii) H OH H H C C C H OH H3C C CH3 H CN H CN 1 (6) Page 13

14 Mark Scheme Wth ½ Wth 0 9. (a) total volume not kept constant (changes, increases) changes concentration of all reactants not just potassium iodide me than one variable changed 1 (b) use me accurate measuring cylinders ( syringes) f smaller volumes in step 1 start timer while adding hydrogen peroxide (when half of the peroxide has been added) put white tile/paper below beaker repeat experiment (any two) 1 (2) Page 14

15 Mark Scheme Wth ½ Wth (a) rate of fward reaction equals rate of backward reaction concentrations of reactant(s) and product(s) are constant 1 rates are constant (b) iodine will go from chlofm layer (bottom layer) into the KI layer (top layer) to reste equilibrium equilibrium moves to left (rate of backward reaction increases) 1 (c) 0.3 g of iodine is dissolved in chlofm 0.3 therefe, concentration = = 30 g l (units not necessary) 1 (3) Page 15

16 Mark Scheme Wth ½ Wth (a) line should go up to + 75 line should then go down to 26 1 (b) (i) heterogeneous 1 (ii) same starting level lower peak same finishing level (c) (i) = 1.2 cm 3 s (-½ f wrong no units) Page 16

17 Mark Scheme Wth ½ Wth 0 11 (c) (ii) 1 mol O2 from 2 mol of H2O2 1 mol H2O2 = 34 g 24 litres O2 from 2 x 34 g of H2O2 68 x litres from = g 24 ( - ½ f wrong no units) 2 (6) Page 17

18 Mark Scheme Wth ½ Wth (a) propane molecules are held together by weak fces ethanol molecules are held together by strong fces (1) the intermolecular fces in propane are van der Waals fces the intermolecular fces in ethanol are hydrogen bonds van der Waals fces are due to momentary displacement of electrons between atoms hydrogen bonding arises because the O-H bond is highly polarised (there is a large difference in the electronegativities of O and H) the small positive charge on H and small negative charge on O strongly attract (4) Page 18

19 Mark Scheme Wth ½ Wth (a) [H + (aq)] = 1 x 10-8 mol l -1 1 (units not necessary) (b) this must be the salt of a strong alkali ( base) and a weak acid alkali stronger than acid 1 (c) HCN CNH 1 (3) Page 19

20 Mark Scheme Wth ½ Wth (a) Seawater (sodium chlide), carbon dioxide, ammonia (- ½ f any omission) crect fmulae 1 (b) CaCO3 CaO + CO2 H = +ve C + O2 CO2 H = -ve 1 use of exothermic/ endothermic (c) Ca(OH)2 + 2NH4Cl CaCl2 + 2H2O + 2NH3 1 Page 20

21 Mark Scheme Wth ½ Wth (d) magnesium carbonate is insoluble magnesium carbonate fms a precipitate 1 (e) CO2 NH3 NH4Cl recycled (reused) coke added to limestone to provide energy by reacting with O2 from air ( by burning) calcium chlide produced as by-product (some) reactants found naturally (easily obtained, cheap) continuous process recycling occurs no waste products non-polluting by-products are useful (any two, 1 mark each) 2 (6) Page 21

22 Mark Scheme Wth ½ Wth (a) hydrolysis (hydrolysing) 1 digestion denaturing (b) (i) NH2 H C H COO 1 (ii) ACB on rhs (igne distances; der must be crect) ABC, BAC, CAB on rhs CBA on lhs (wth 1 mark) 2 BCA CBA on rhs (4) Page 22

23 Mark Scheme Wth ½ Wth (a) Q = It = 0.5 x 14 x 60 = 420 C 2H + + 2e - H2 n = 2 2 x C 1 mol H2 420 C litres 2 x x C x = litres ( ½ f wrong no units) 3 (b) add variable resist (to keep current constant) use platinum electrodes 1 add a device to keep constant current (4) [END OF MARKING INSTRUCTIONS] Page 23

2017 Chemistry. National 5. Finalised Marking Instructions

2017 Chemistry. National 5. Finalised Marking Instructions National Qualifications 2017 2017 Chemistry National 5 Finalised Marking Instructions Scottish Qualifications Authity 2017 The infmation in this publication may be reproduced to suppt SQA qualifications