2005 Chemistry. Advanced Higher. Finalised Marking Instructions

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1 2005 Chemistry Advanced Higher Finalised Marking Instructions These Marking Instructions have been prepared by Examination Teams for use by SQA Appointed Markers when marking External Course Assessments.

2 Advanced Higher Chemistry General information for markers The general comments given below should be considered during all marking. Marks should not be deducted for incorrect spelling or loose language as long as the meaning of the word(s) is conveyed. Example: Answers like 'distilling' (for 'distillation') and 'it gets hotter' (for 'the temperature rises') should be accepted. 2 A right answer followed by a wrong answer should be treated as a cancelling error and no marks should be given. Example: What is the colour of universal indicator in acid solution? The answer 'red, blue' gains no marks. 3 If a right answer is followed by additional information which does not conflict, the additional information should be ignored, whether correct or not. Example: Why can the tube not be made of copper? If the correct answer is related to a low melting point, and the candidate s answer is 'It has a low melting point and is coloured grey' this would not be treated as a cancelling error. 4 Full marks should be awarded for the correct answer to a calculation on its own whether or not the various steps are shown unless the question is structured or working is specifically asked for. 5 A mark should be deducted in a calculation for each arithmetic slip unless stated otherwise in the marking scheme. No marks should be deducted for incorrect or missing units at intermediate stages in a calculation. 6 A mark should be deducted for incorrect or missing units unless stated otherwise in the marking scheme. Please note, for example, that KJ mol - is not acceptable for kj mol - and a mark should be deducted. 7 Where a wrong numerical answer (already penalised) is carried forward to another step, no further penalty is incurred provided the result is used correctly. 8 No mark is given for the solution of an equation which is based on a wrong principle. Example: Use the information in the table to calculate the standard entropy change for the reaction: C 2 H 2 + 2HCl CH 2 ClCH 2 Cl Compound Sº/J K - mol - C 2 H 2 20 HCl 87 CH 2 ClCH 2 Cl 208 Using Sº = Sº reactions - Sº products would gain zero marks. Page 2

3 9 No marks are given for the description of the wrong experiment. 0 Full marks should be given for correct information conveyed by a sketch or diagram in place of a written description or explanation. In a structural formula, if one hydrogen atom is missing but the bond is shown, no marks are deducted. Examples: H H O H C C O C C H H H H Would not be penalised as the structural formula for ethyl ethanoate. If the bond is also missing, then zero marks should be awarded. Example: H H O H C C O C C H H H H 2 If a structural formula is asked for, CH 3 and CH 3 CH 2 are acceptable as methyl and ethyl groups respectively. 3 With structures involving an OH or an NH 2 group, no mark should be awarded if the 'O' or 'N' are not bonded to a carbon, ie OH CH 2 and NH 2 CH 2. 4 When drawing structural formulae, no mark should be awarded if the bond points to the 'wrong' atom, eg C C OH 5 A symbol or correct formula should be accepted in place of a name unless stated otherwise in the marking scheme. 6 When formulae of ionic compounds are given as answers it will only be necessary to show ion charges if these have been specifically asked for. However, if ion charges are shown, they must be correct. If incorrect charges are shown, no marks should be awarded. 7 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 for 'burning' since the word 'burned' appears in the text. Page 3

4 8 A guiding principle in marking is to give credit for (partially) correct chemistry rather than to look for reasons not to give marks. Example : 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. Although not completely correct, the answer, '3, methyl-hexane' would gain the full mark ie wrong use of commas and dashes. Example 2: A student measured the ph of four carboxylic acids to find out how their strength is related to the number of chlorine atoms in the molecule. The results are shown. Structural formula ph CH 3 COOH 65 CH 2 ClCOOH 27 CHCl 2 COOH 0 90 CCl 3 COOH 0 5 How is the strength of the acids related to the number of chlorine atoms in the molecule? Again, although not completely correct, an answer like 'the more Cl 2, the stronger the acid' should gain the full mark. Example 3: Why does the (catalytic) converter have a honeycomb structure? A response like 'to make it work' may be correct but it is not a chemical answer and the mark should not be given. Page 4

5 2005 Chemistry Advanced Higher Marking scheme. C 2. A 2. A 22. C 3. D 23. A 4. B 24. B 5. C 25. C 6. C 26. D 7. A 27. B 8. D 28. A 9. D 29. A 0. B 30. C. D 3. C 2. C 32. D 3. D 33. C 4. B 34. D 5. A 35. A 6. B 36. C 7. A 37. B 8. A 38. D 9. B 39. B 20. B 40. C Page 5

6 Marking Instructions Chemistry Advanced Higher Section B Question (a) (i) Superconductor A conductivity increases. Must specify which. Answer in terms of resistance (but not a cancelling error) (ii) Semiconductor B conductivity decreases for both increase or both decrease (b) n-type, N-type or just n P-type and correct explanation for p-type Must be singular P has more e - /spare e - / surplus e - P contains more outer electrons than Si Phosphorus contains 5 outer electrons Phosphorus contains an extra (outer) electron P contains an extra electron in the conductance band P-type and correct explanation for n-type Page 6

7 2 (a) Amphoteric (b) Covalent network/lattice/macromolecule Polar covalent network/lattice/macromolecule Covalent molecular One part only correct covalent crystals (c) (i) Temperatures below 750 K or other acceptable values which fit into this range º K (ii) Change of state/increase in entropy Magnesium boils/changes into a gas/melts Any change of state in which entropy increases (but not (aq)) So s l or l g Change of chemical state g l x l s x Page 7

8 3 (a) Both ammonia and water are electron pair donors can form dative (covalent) bonds free electrons Their molecules have lone pairs of electrons/free electron pairs or non bonding pairs 2 unpaired electrons (b) s 2 2s 2 2p 6 3s 2 3p 6 3d 6 [Ne] 3s 2 3p 6 3d 6 Ignore 4s 0 Correct orbital box notation indicating which orbitals are involved [Ar]3d 6 (c) (i) 2H 2 O(l) O 2 (g) + 4H + (aq) + 4e - (or multiples) States not required Negative sign on electron not required Equation reversed (ii) G o = -nfe o G = -nfe = - 4 x x 0 58 = (kj mol - ) Answer given as without working = 2/3 If n = 3, Gº = kj mol - (2/3) n = 2, Gº = - 9 kj mol - (2/3) n =, Gº = kj mol - (2/3) If given as +ve values, then (/3) J mol - Or correct answer in J mol - G = + nfe deduct only Page 8

9 4 (a) Ca + (g) + e - + 2H(g) (states must be present) (b) kj or kj mol - or -46 kj KJ mol - no units (c) (kj mol - ) Units not required. Following on from in (b) gives here () (allow follow through from wrong answer in (b)) but only if in (b) even if 3 kj given as answer to (b) (d) Calcium hydroxide and hydrogen or Ca(OH) 2 and H 2 Correct formulae acceptable in place of names CaO No names, wrong formulae Page 9

10 5 (a) (i) Hexachloroplatinate(IV) Hexachloroplatinumate(IV) ite (IV) (ii) [PtCl 6 ] K = [PtCl 2 (organic) 2 6 ] (aq) No brackets at all Need both states (iii) No effect (b) Tertiary Page 0

11 6 (a) (i) n = V x C = x 0 05 = 7 6 x 0-4 (ii) 7 6 x 0-4 x 2 x 0 = 52 x 0-2 (allow follow through if answer to (i) has been multiplied by 20 correctly) 5 x 0-2 Need to follow through from wrong answers to (i) and (ii) (iii) Answer to (iii) x 30 gives answer to (iv) Moles of NaOH started with = V x C = x = Moles of NaOH reacted with aspirin = = (Allow follow through) (iv) Moles of aspirin = /2 = Mass of aspirin = x 80 = 0 882g 0 9 (b) Average mass of aspirin in each tablet = = 0 294g 3 = 0 300g Aspirin is insoluble in water Aspirin is not very soluble in water Aspirin is more soluble in alkaline solution (c) Check its melting point/mixed MP Colorimetry/IR/nmr/spectroscopy/thin layer chromatography Boiling point but not a cancelling error Page

12 7 (a) +5/5/V Fifth oxidation state (b) (i) st order wrt [BrO - 3 ] Must give order st order wrt [Br - ] 2 nd order wrt [H + ] (all 3 required) (ii) Rate = k [BrO 3 - ] [Br - ] [H + ] 2 k must be lower case allow follow through from (i) Rate α 4 th order K instead of k (iii) k = [BrO Rate ][Br ][H ] but must follow on from answer to (ii) = 8 Units = l 3 mol -3 s - Page 2

13 8 (a) ClO - or ClO - (aq) hypochlorite Chlorine oxide CLO - C&O (b) K a = + [ H O ][ ClO ] 3 [ HClO] H+ instead of H 3 O [H 2 O] in equation no brackets or curved brackets (c) [H + ] = 3 98 x 0-6 (from ph = -log 0 [H + ] ) [ ClO ] [ HClO] [ H ] = /3 98 = K a / 0 = 0 0 (or /00) Can also work out from [ salt] ph = pk a + log [ acid] in which case calculating pk a = 7 4 is worth mark Page 3

14 9 (a) (i) Sodium or any other Group I metal Accept Ba (ii) Acidified dichromate/permanganate (Hot) copper oxide/copper (II) oxide any other suitable oxidising agent Tollens, Benedict s, Fehlings reagents Copper (I) oxide (b) CH 3 CH 2 OCH 2 CH 3 or C 2 H 5 instead of CH 3 CH 2 H H H H H C C O C C H H H H H If full SF drawn then all bonds should be drawn correctly. Allow as a slip H missing as long as bond is given (c) Bonds Broken( H +ve) Bonds made ( H -ve) x C = C (+602) 2 x C Cl (-652) x Cl Cl (+243) x C C (-346) H = = -53 kj mol - or kj First mark for values in brackets (ignore signs) Page 4

15 0 (a) (Electrophilic) Substitution Nucleophilic Substitution (b) Dilute acid H + /H 2 O H 2 O on its own Concentrated acid Acid hydrolysis (c) CH 3 CH 2 CHCH 3 Immediate environment around the chiral C atom must be correct C H H 3 C HO C O Page 5

16 (a) mark for intermediate mark for final product Solid lines ok but must have charge on central C or outside the brackets. Charge on OH in intermediate OH C HO: CH 2 CH 2 CH 3 CH 2 CH 2 CH 3 2 C HO C Cl H Cl CH 3 H CH 3 Accept any correct structure for pentan-2-ol (for 2 nd mark) CH 2 CH 2 CH 3 C HO CH 3 H + Cl (b) cis pent-2-ene H H C C H 3 C C 2 H 5 trans pent-2-ene H 3 C H C C H C 2 H 5 Page 6

17 2 (a) Parts underlined (or equivalent) must be given General definition of an antagonist Antagonists because they inhibit bacterial wall synthesis (b) O Any errors in the structure C NH S CH 3 O N CH 3 COOH Can be omitted or joined to another C Page 7

18 3 (a) C=O or carbonyl Carboxyl Or COOH (b) Element C H O Mass RAM 2 6 N o moles Mole ratio Simplest ratio Empirical formula = C 7 H 6 O 2 Can work out % composition to show empirical formula eg or can be done as 84 %C = x 00 = 68 9% % of 22 = 84 C 7 6 %H = x 00 = 4 9% 4 9% of 22 = 6 H %O = x 00 = 26 2% 26 2% of 22 = 32 O2 22 (c) (i) C 7 H 6 O 2 C 6 H 5 COOH (ii) C 6 H 5 + phenyl -ve charge Page 8

19 (d) O OH C COOH O Page 9

20 3 (e) _ E= Lhcv = (6 02 x 0 23 )(6 63 x 0-34 )(3 x 0 8 )( 685 x 0 5 ) 0 3 = kj mol - (20 2 kj mol - ) units not required or if calculate frequency first Lhc If use E = () but use 685 as wavelength then answer λ will be 7 06 x 0-8 kj mol - () only If don t change cm - to m -, E = kj mol - (2/3) or change cm - to m - wrongly, E = kj mol - (2/3) If don t change J to kj, E = 2076 kj mol - or 2076 J mol - (2/3 for either) If don t change cm - to m - and J to kj, E = kj mol - (/3) If L omitted, then mark for 3 35 x 0-23 but zero for 3 35 x 0-20 kj mol - [END OF MARKING INSTRUCTIONS] Page 20

2011 Chemistry. Advanced Higher. Finalised Marking Instructions

2011 Chemistry. Advanced Higher. Finalised Marking Instructions 20 Chemistry Advanced igher Finalised Marking Instructions Scottish Qualifications Authority 20 The information in this publication may be reproduced to support SQA qualifications only on a non-commercial