20 8 Transition metals form complex ions. (a) Complex ions have a central metal ion surrounded by ligands. (i) Give a reason why the ammonium ion cannot act as a ligand. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (ii) Explain why the complex ions [Co(NH3)6]2+ and [Co(H2O)6]2+ are coloured and have different colours. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (b) Which of these complexes is used in the treatment of cancer? (1) A OH2 H2O Pt Cl Cl B OH2 Cl Pt Cl OH2 C NH3 Cl Pt Cl NH3 D OH2 H3N Pt Cl Cl Turn over 21 (c) Compare and contrast the complex ions formed by cobalt(III) ions with the ligand ethane‑1,2‑diamine and with the ligand EDTA4–. Ignore any difference in colour. H2N NH2 O –O O– –O O O– O N N O ethane‑1,2‑diamine EDTA4– (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 22 (d) Hydrated chromium(III) chloride, CrCl3.6H2O, dissolves in water to form a number of different complex ions containing both chloride and water ligands. The general formula of these complex ions is [Cr(H2O)x(Cl)y](3–y)+ In an experiment, 0.10 mol of a complex reacted with excess silver nitrate solution to produce 0.20 mol of silver chloride. Chloride ions which are ligands within the complex do not react with silver nitrate. Deduce the formula of this chromium(III) complex ion. Justify your answer. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 8 = 12 marks)