An excess of aqueous ammonia is added to a solution containing the complex ion [Co(H₂O)₆]²⁺. [Co(H₂O)₆]²⁺ + 6NH₃ ⇌ [Co(NH₃)₆]²⁺ + 6H₂O

1. (a)Complete the sentence to describe the colour change that will be seen during this reaction. The colour changes from _______________ to _______________.[1]
2. (b)Write an expression for the stability constant, Kstab, of [Co(NH₃)₆]²⁺.[1]
3. (c)The numerical value of Kstab of [Co(NH₃)₆]²⁺ is 7.7 × 10⁴. What deduction about the properties of [Co(NH₃)₆]²⁺ and [Co(H₂O)₆]²⁺ can be made from this Kstab value?[1]
4. (d)(i)Oxygen can oxidise [Co(NH₃)₆]²⁺ to [Co(NH₃)₆]³⁺ under standard conditions in alkaline solutions. [Co(NH₃)₆]³⁺ + e⁻ ⇌ [Co(NH₃)₆]²⁺ E° = +0.10V Use this information and the Data Booklet to calculate the E°cell value for this oxidation of [Co(NH₃)₆]²⁺.[1]
5. (d)(ii)Write an ionic equation for this oxidation of [Co(NH₃)₆]²⁺.[1]
6. (d)(iii)Predict, by selecting suitable data from the Data Booklet, whether oxygen can oxidise Co²⁺(aq) in acidic solution, in the absence of ammonia. Explain your answer.[2]