Transition metals and their chemistry

Sample questions

Original practice questions written in the style of the exam.

1. Question 14 marks

   Explain why aqueous solutions of transition metal complex ions such as $[\text{Cu}(\text{H}_2\text{O})_6]^{2+}$ are coloured.

   Mark scheme

   • The ligands cause the 3d orbitals to split into two groups at different energies (1)
   • An electron absorbs energy from visible light and is promoted to a higher-energy d orbital (1)
   • The frequency absorbed is given by $\Delta E = hf$ (1)
   • The remaining frequencies are transmitted (or reflected), and these give the colour seen (1)
2. Question 24 marks

   Concentrated hydrochloric acid is added to aqueous copper(II) sulfate until no further change occurs.

   Give the formula of the copper-containing product and state the colour change. Describe and explain the change in shape of the complex ion.

   Mark scheme

   • $[\text{CuCl}_4]^{2-}$ (1)
   • Blue to yellow (accept yellow-green, as an intermediate green may be seen) (1)
   • Shape changes from octahedral to tetrahedral (1)
   • Chloride ions are larger than water molecules, so only four fit around the $$ ion (1)