a. Write expressions for the stability constants for the following reactions:

i. [PtCl₄]^2–(aq) + 2NH₃(aq) → PtCl₂(NH₃)₂(aq) + 2Cl^–(aq)

ii. [Cr(H₂O)₆]³⁺(aq) + 2Cl^–(aq) → [Cr(H₂O)4Cl₂]+(aq) + 2H₂O(l)

iii. [Ni(H₂O)₆]²⁺(aq) + 4NH₃(aq) → [Ni(NH₃)₄(H₂O)₂]²⁺(aq) + 4H₂O(l)

b. An iron(III) ion, Fe³⁺, in aqueous solution has six water molecules bonded to it as ligands.

i. Draw the structure of this ion.

ii. When thiocyanate ions, SCN^–, are added to an aqueous solution of iron(III) ions, the solution turns red and one water molecule is replaced by a thiocyanate ion. Use the concept of stability constants to explain why the reaction occurs.

iii. Deduce the formula of the ion forming the red solution.

iv. The stability constant for aqueous Fe³⁺ ions with SCN^– as a ligand is 891 dm₃ mo^l–1. The stability constant for aqueous Fe³⁺ ions with fluoride ions, F^–, as a ligand is 2 × 10⁵ dm³ mol^–1. A solution containing fluoride ions is added to the red solution. Would you expect to observe any changes? Explain your answer.