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9701/42

Chemistry 9701/42 — October/November 2019

Cambridge A-Level · A Level Structured Questions · worked solutions for every part, with the mark scheme

9
questions
100
marks
120
minutes

Topics Carboxylic Acids and Derivatives · Electrochemistry · Chemical Energetics · Nitrogen Compounds · Analytical Techniques · Reaction Kinetics · +8 more

Q1ElectrochemistryFree sample

An electrochemical cell is constructed using two half-cells.

● a Br2/Br−\text{Br}_2/\text{Br}^- half-cell
● an Mn3+/Mn2+\text{Mn}^{3+}/\text{Mn}^{2+} half-cell

(a)

State the material used for the electrode in each half-cell.

Br2/Br−\text{Br}_2/\text{Br}^- half-cell

Mn3+/Mn2+\text{Mn}^{3+}/\text{Mn}^{2+} half-cell

1M
(b)

The cell is operated at 298 K298\text{ K}.

The Br2/Br−\text{Br}_2/\text{Br}^- half-cell has standard concentrations.

The Mn3+/Mn2+\text{Mn}^{3+}/\text{Mn}^{2+} half-cell has [Mn3+]=0.500 mol dm−3[\text{Mn}^{3+}] = 0.500\text{ mol dm}^{-3} and [Mn2+]=0.100 mol dm−3[\text{Mn}^{2+}] = 0.100\text{ mol dm}^{-3}.

(i)

Use the Nernst equation to calculate the electrode potential, EE, of the Mn3+/Mn2+\text{Mn}^{3+}/\text{Mn}^{2+} half-cell under these conditions.

2M
(ii)

Calculate the EcellE_{\text{cell}} under these conditions.

1M
(iii)

Write an equation for the overall cell reaction that occurs.

2M
(c)

An aqueous solution of copper(II) sulfate is electrolysed using copper electrodes. A current of 1.50 A1.50\text{ A} is passed for 3.00 hours3.00\text{ hours}. 5.09 g5.09\text{ g} of copper is deposited on the cathode.

The charge on one electron is −1.60×10−19 C-1.60 \times 10^{-19}\text{ C}.

The relative atomic mass of copper is 63.563.5.

Use these data to calculate an experimentally determined value for the Avogadro constant, LL.
Give your answer to three significant figures.

5M
(d)

Explain why magnesium metal cannot be obtained by the electrolysis of dilute aqueous magnesium sulfate. Your answer should include data from the Data Booklet.

2M

The rest of this paper

8 more questions
  • Q2Reaction Kinetics9M
  • Q3Equilibria8M
  • Q4Chemical Energetics6M
  • Q5Group 2 · Chemical Energetics13M
  • Q6Transition Elements · Electrochemistry12M
  • Q7Polymerisation · Carboxylic Acids and Derivatives · Hydrocarbons · Nitrogen Compounds13M
  • Q8Halogen Compounds · Organic Synthesis · Carboxylic Acids and Derivatives · Analytical Techniques14M
  • Q9Introduction to A Level Organic Chemistry · Carboxylic Acids and Derivatives · Nitrogen Compounds · Analytical Techniques12M
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