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CIE Nov 2013 v2 Paper 4 Q3
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![Examiners For Use (a) (i) Using the symbol HZ to represent a Brnsted-Lowry acid, write equations which show the following substances acting as Brnsted-Lowry bases. NH3 + CH3OH + (ii) Using the symbol B to represent a Brnsted-Lowry base, write equations which show the following substances acting as Brnsted-Lowry acids. NH3 + CH3OH + [4] (b) State brie y what is meant by the following terms. (i) reversible reaction(ii) dynamic equilibrium[2] (c) (i) Explain what is meant by a buffer solution.(ii) Explain how the working of a buffer solution relies on a reversible reaction involving a Brnsted-Lowry acid such as HZ and a Brnsted-Lowry base such as Z.[4]UCLES 2013 9701/42/O/N/13<br />
Examiners For Use (d) Propanoic acid, CH3CH2CO2H, is a weak acid with Ka = 1.34105 mol dm3. (i) Calculate the pH of a 0.500 mol dm3 solution of propanoic acid. Buffer solution F was prepared by adding 0.0300 mol of sodium hydroxide to 100 cm3 of a 0.500 mol dm3 solution of propanoic acid. (ii) Write an equation for the reaction between sodium hydroxide and propanoic acid.(iii) Calculate the concentrations of propanoic acid and sodium propanoate in buffer solution F. [propanoic acid] =mol dm3 [sodium propanoate] =mol dm3 (iv) Calculate the pH of buffer solution F. pH =[6] (e) Phenyl propanoate cannot be made directly from propanoic acid and phenol. Suggest the identities of the intermediate G, the reagent H and the by-product J in the following reaction scheme. ONa CH3CH2CO2H G isH isJ isUCLES 2013 9701/42/O/N/13 [2] [Total: 18] [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/November_2013_v2_QP_-_Paper_4_CIE_Chemistry_A-level_3-0.jpg)
![Page 4 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 42 (a) (i) NH3 + HZNH4 + Z CH3OH + HZCH3OH2 + Z (ii) NH3 + BNH2 + BH CH3OH + BCH3O + BH (b) (i) a reaction that can go in either direction (ii) rate of forward = rate of backward reaction or forward/back reactions occurring but concentrations of all species do not change [1] [1] [1] [1] [1] [4] [1] [2] [1] [1] [1] [1] [1] [5 max 4] [1] ecf [1] [1] [1] [1] [6] [2] [Total: 18] (c) (i) a solution that resists changes in pH when small quantities of acid or base/alkali are added (ii) in the equilibrium system HZ + H2O ! Z + H3O addition of acid: reaction moves to the left or H combines with Z and forms HZ addition of base: the reaction moves to the right combines with OH and more Z formed or H (d) (i) [H ] = (0.51.3410 ) = 2.5910 (mol dm pH = 2.59/2.6 (min 1 d.p) (ii) CH3CH2CO2H + NaOHCH3CH2CO2Na + H2O (iii) n(acid) in 100 cm = 0.5100/1000 = 0.05 mol n(acid) remaining = 0.050.03 = 0.02 mol [acid remaining] = 0.2 (mol dm likewise, n(salt) = 0.03 mol [salt] + 0.3 (mol dm (iv) pH = 4.87 + log(0.3/0.2) = 5.045.05 ecf [1] (e) G is CH3CH2COCl H is SOCl 2 or PCl J is NaCl (or corresponding Br compounds for G, H and J; CH3CH2COBr, SOBr2, NaBr)Cambridge International Examinations 2013<br />](https://learnah.org/wp-content/uploads/2018/08/November_2013_v2_MS_-_Paper_4_CIE_Chemistry_A-level_3.jpg)