This question is about a reversible reaction.
The reaction between hydrated copper(II) ions, [Cu(H2O)6]2+[\text{Cu(H}_2\text{O)}_6]^{2+}[Cu(H2O)6]2+, and chloride ions, Cl−\text{Cl}^-Cl−, is reversible.
The ionic equation for the reaction is:
[Cu(H2O)6]2+(aq)+4Cl−(aq)⇌[CuCl4]2−(aq)+6H2O(l) [\text{Cu(H}_2\text{O)}_6]^{2+}(\text{aq}) + 4\text{Cl}^-(\text{aq}) \rightleftharpoons [\text{CuCl}_4]^{2-}(\text{aq}) + 6\text{H}_2\text{O}(\text{l}) [Cu(H2O)6]2+(aq)+4Cl−(aq)⇌[CuCl4]2−(aq)+6H2O(l)At room temperature, the colour of the reactants and products are as follows:
The colour of the equilibrium mixture is green at room temperature.
Give the name of the solvent used to dissolve the ions to make the aqueous solutions in this reaction.
A few drops of a concentrated hydrochloric acid solution (providing a high concentration of Cl−\text{Cl}^-Cl−) are added to the green equilibrium mixture. Explain the colour change observed.
When a test tube containing the green equilibrium mixture is placed in an ice bath, the mixture becomes blue. Explain what this shows about the energy change for the forward reaction.
Explain why a change in pressure does not affect the colour of the equilibrium mixture.
Other metal ions form coloured complex ions with ligands in aqueous solutions. Which metal ion could form a coloured equilibrium mixture when combined with suitable ligands?
21 exam-style questions on AQA GCSE Chemistry 6.2 Reversible reactions and dynamic equilibrium, covering 6.2.1 Reversible reactions, 6.2.2 Energy changes and reversible reactions, 6.2.3 Equilibrium, 6.2.4 The effect of changing conditions on equilibrium (HT only), 6.2.5 The effect of changing concentration (HT only), 6.2.6 The effect of temperature changes on equilibrium (HT only), and 6.2.7 The effect of pressure changes on equilibrium (HT only). Each one has a worked solution and a mark scheme showing where the marks go.