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Transition metals (A-level only)

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Question 24

A student performs an experiment to determine the percentage of copper in a cupronickel coin.

The student:

  • reacts a 1.60 g1.60\text{ g}1.60 g sample of the coin with concentrated nitric acid (the copper in the alloy reacts completely to form aqueous copper(II) ions, while the nickel forms nickel(II) ions which do not interfere with this titration)
  • transfers the resulting solution to a volumetric flask and makes the volume up to 500 cm3500\text{ cm}^3500 cm3 with distilled water
  • shakes the flask thoroughly
  • transfers a 25.0 cm325.0\text{ cm}^325.0 cm3 portion of this solution to a conical flask and adds an excess of potassium iodide
  • titrates the mixture with 0.0500 mol dm−30.0500\text{ mol dm}^{-3}0.0500 mol dm−3 sodium thiosulfate (Na2S2O3\text{Na}_2\text{S}_2\text{O}_3Na2​S2​O3​) solution, requiring exactly 18.40 cm318.40\text{ cm}^318.40 cm3 to react with all the iodine produced.

The equations for the reactions are:

2Cu2+(aq)+4I−(aq)→2CuI(s)+I2(aq) 2\text{Cu}^{2+}(aq) + 4\text{I}^-(aq) \rightarrow 2\text{CuI}(s) + \text{I}_2(aq) 2Cu2+(aq)+4I−(aq)→2CuI(s)+I2​(aq) 2S2O32−(aq)+I2(aq)→2I−(aq)+S4O62−(aq) 2\text{S}_2\text{O}_3^{2-}(aq) + \text{I}_2(aq) \rightarrow 2\text{I}^-(aq) + \text{S}_4\text{O}_6^{2-}(aq) 2S2​O32−​(aq)+I2​(aq)→2I−(aq)+S4​O62−​(aq)
a.

Calculate the percentage of copper by mass in the cupronickel coin. Give your answer to the appropriate number of significant figures.

[5]
b.

Give the full electron configuration of a copper(I) ion.

[1]
c.

Copper(I) chloride is a white solid. Explain why copper(I) compounds are white whereas copper(II) compounds are typically coloured.

[3]
Markscheme

Transition metals (A-level only) Questions

  1. A Level
  2. /Chemistry
  3. /Transition metals (A-level only)

63 exam-style questions on AQA A Level Chemistry Transition metals (A-level only), covering General properties of transition metals (A-level only), Substitution reactions (A-level only), Shapes of complex ions (A-level only), Formation of coloured ions (A-level only), Variable oxidation states (A-level only), and Catalysts (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.

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