CIE Jun 2016 v2 Paper 4 Q2

Answers available below

Ethanoic acid is a weak acid. PMT (a) Explain what is meant by the term weak acid.[1] (b) The pKa values of four acids are listed below. acid 1 2 3 4 structural formula CH3CO2H CH3CH2CO2H CH3CHCl CO2H CH2Cl CH2CO2H pKa 4.8 4.9 2.8 4.0 (i) State the mathematical relationship between pKa and the acid dissociation constant Ka.[1] (ii) With reference to acidity, explain the difference in pKa values between acid 1 and acid 2,acid 2 and acid 3,acid 3 and acid 4.[3]UCLES 2016 9701/42/M/J/16<br />
 (c) (i) Draw a fully labelled diagram of the equipment needed to measure the voltage of an electrochemical cell consisting of the standard hydrogen electrode and the standard Cu / Cu2+ electrode. PMT (ii) For the cell drawn in (i), calculate the and state which electrode is positive. [4] =identity of the positive electrode[1] (d) A monobasic acid, D, has Ka = 1.23105 mol dm3. (i) Calculate the pH of a 0.100 mol dm3 solution of D. (ii) An electrochemical cell similar to the one you have drawn in (c)(i) was set up using a 0.100 mol dm3 solution of D in the hydrogen electrode instead of the standard solution. Use the data and the Nernst equation, E = E o + 0.059 log [H+(aq)], to calculate the new E cell in this experiment. pH =[2]UCLES 2016 9701/42/M/J/16 E cell =V [2] [Total: 14] [Turn over<br />

Show answer