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CIE Nov 2014 v3 Paper 4 Q4
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![(a) The following circuits were set up using aqueous hydrochloric and aqueous ethanoic acids as electrolytes. Assume that the two circuits were identical apart from the electrolyte. PMT bulb graphite electrodes switch bulb switch 1 mol dm3 HCl (aq) graphite electrodes 1 mol dm3 CH3CO2H(aq) When the switches were closed, bulb 1 was brighter than bulb 2. Explain why.[2] (b) (i) State what is meant by a buffer solution.(ii) Outline how a buffer solution can be prepared from ethanoic acid and a named base.[4] (c) Amino acids such as alanine, CH3CH(NH2)CO2H, can act as a buffer solution. Construct two equations to illustrate this. equation 1 equation 2UCLES 2014 9701/43/O/N/14 [2]<br />
PMT (d) Tartaric acid is present in many plants. OH HO OH OH tartaric acid (i) Tartaric acid has two dissociation constants, K1 and K2, for which the pKa values are 2.99 and 4.40. Suggest equations showing the two dissociations that give rise to these pKa values. pKa 2.99 pKa 4.40 (ii) One stereoisomer of tartaric acid is shown. HO HO2C CO2H OH Complete the diagrams showing two other stereoisomers of tartaric acid. CO2H CO2HUCLES 2014 9701/43/O/N/14 [4] [Total: 12] [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/November_2014_v3_QP_-_Paper_4_CIE_Chemistry_A-level_4-0.jpg)
![Page 4 Mark Scheme Syllabus Paper Cambridge International A LevelOctober/November 2014 9701 43 (b) (i) pale blue precipitate A Cu(OH)2 OR [Cu(OH)2(H2O)4] solution B solution C (ii) solution B solution C [Cu(NH3)4(H2O)2] OR [Cu(NH3)4] 2+ 2+ [CuCl 4] 2 royal / deep / dark blue OR violet-blue yellow / green (iii) redox OR oxidation of Cu OR reduction of Cu AND reducing agent / reductant 2+ (c) (d) 3d-shell is full / 3d 10 / no vacant d-orbital / d-orbitals full electrons cannot move between orbitals OR transitions cannot occur green / yellow orange / red AND blue / violet light is absorbed (a) (HCl) stronger acid / more dissociated / ionised in solution (HCl has) more ions / higher concentration of ions (b) (i) A solution that resists changes in the pH / keeps pH fairly constant when small quantities / amounts / vols of acid / H or base / OH are added (ii) add (ethanoic acid) to NaOH OR an equation excess (ethanoic acid) OR mix with sodium ethanoate (c) CH3CH(NH2)COOH + H CH3CH(NH3 )COOH CH3CH(NH2)COOH + OH CH3CH(NH2)COO + H2OCambridge International Examinations 2014 PMT [6] [2] [2] [2] [4] [2]<br />
Page 5 Mark Scheme Syllabus Paper Cambridge International A LevelOctober/November 2014 9701 43 (d) (i) OH OH pKa 2.99 OH OH OH + H+ OH OH OH OH pKa 4.40 OH -O + H+ OH OH (ii) OH HOOC COOH OH OH HOOC COOH OH (S,R) (R,S) OH HOOC (R,R) COOH OH any two of the above (a) any five of these seven points.-bonds are between C-C OR C-Hcarbons are sp rings of charge above and below the ring must be in diagrampresence of -bondselectrons/bonds are delocalisedplanar molecule/bond angles 120 PMT [4]all C-C are the same length/have intermediate bond length between C-C & C=C [5]Cambridge International Examinations 2014<br />](https://learnah.org/wp-content/uploads/2018/08/November_2014_v3_MS_-_Paper_4_CIE_Chemistry_A-level_4-0.jpg)
