Redox chemistry and Groups 1, 2 and 7

Sample questions

Original practice questions written in the style of the exam.

1. Question 14 marks

   Chlorine water is added to aqueous potassium iodide. The mixture is then shaken with cyclohexane and left to separate.

   (a) State what is seen in the aqueous solution and in the cyclohexane layer.

   (b) Write the ionic equation for the reaction.

   (c) Explain, in terms of atomic structure, why chlorine is a stronger oxidising agent than iodine.

   Mark scheme

   • (a) Aqueous solution turns from colourless to brown (1)
   • (a) Cyclohexane (upper) layer turns purple/violet (1)
   • (b) $\text{Cl}_2 + 2\text{I}^- \rightarrow 2\text{Cl}^- + \text{I}_2$ (1)
   • (c) Chlorine atoms are smaller with less shielding, so the incoming electron is more strongly attracted to the nucleus (1)
2. Question 23 marks

   Describe and explain the trend in thermal stability of the Group 2 carbonates from magnesium carbonate to barium carbonate.

   Mark scheme

   • Thermal stability increases down the group (decomposition needs higher temperatures) (1)
   • The cation radius increases (same charge), so the charge density of the cation decreases (1)
   • So the cation polarises (distorts) the carbonate ion's electron cloud less, weakening its $\text{C{-}O}$ bonds less (1)