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CIE Jun 2016 v3 Paper 4 Q4
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![(a) (i) Define the term standard cell potential, PMT[1] The following incomplete diagram shows the apparatus that can be used to measure the for a cell composed of the Fe3+ / Fe2+ and Ag+ / Ag half-cells. (ii) Complete the diagram, labelling the components you add. [1] (iii) Identify the components A-D. ABCD[3] (b) (i) Use E o values to write an equation for the cell reaction that takes place if the two electrodes in (a) are connected by a wire and the circuit is completed.[1] (ii) Another electrochemical cell was set up using 0.31 mol dm3 Ag+(aq) instead of the standard Ag solution. Use the Nernst equation, E = E o + 0.059 log [Ag+(aq)], and the relevant E o values to calculate the new E cell in this experiment.UCLES 2016 9701/43/M/J/16 E cell =V [2] [Total: 8]<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v3_QP_-_Paper_4_CIE_Chemistry_A-level_4.jpg)
![Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A LevelMay/June 2016 9701 43 Question Answer Marks PMT (a) (i) SCP is the EMF / potential of a cell composed of two electrodes (OR half cells) under standard conditions (OR at 289 K OR 1 mol dm 3 (ii) voltmeter and salt bridge (iii) A is Ag (aq) or AgNO3(aq) B is Ag C is Pt D is Fe 2+ 3+ (aq) and Fe (aq) (combination of A and B can be reversed with combination of C and D) (b) (i) 2+ 3+ Ag + FeAg + Fe (ii) E = E + 0.059log [Ag cell = 0.770.77 = 0.0 V so E ] = 0.800.03 = 0.77 V (a) (i) pKa = log K (ii) diacids are more acidic than CH3CO2H HO2C group is electron-withdrawing, stabilising the monoanion OR HO2C group is electron-withdrawing, weakening the OH bond OR monoanion is stabilised by Hbonding as n increases, the electronwithdrawing group is further away from the ionising CO2H group OR the (intervening) alkyl groups destabilise the anion (iii) removing H from an anion is not electrostatically favourable (b) (i) a solution which resists changes in pH when small amounts of H or OH are addedCambridge International Examinations 2016 [1] [1] [3] [1] [1] [1] [Total: 8] [1] [1] [1] [1] [1] [1] [1]<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v3_MS_-_Paper_4_CIE_Chemistry_A-level_4.jpg)