Bubbling air through different aqueous mixtures of CoCl₂, NH₄Cl and NH₃ produces various complex ions with the general formula [Co(NH₃)₆₋nClₙ]³⁻ⁿ.

1. (a)(i)Determine the oxidation state of the cobalt in these complex ions.[1]
2. (a)(ii)Name the two types of reaction undergone by the cobalt ions during the formation of these complex ions.[2]
3. (a)(iii)The complex [Co(NH₃)₄Cl₂]⁺ shows isomerism. Draw three-dimensional structures of the two isomers, and suggest the type of isomerism shown here. [Figure X.X] type of isomerism ______________[3]
4. (b)(i)What is meant by the term co-ordination number?[1]
5. (b)(ii)Complete the table by predicting appropriate co-ordination numbers, formulae and charges for the complexes C, D, E and F. [Figure X.X][6]
6. (c)(i)Iron(III) forms complexes in separate reactions with both SCN⁻ ions and Cl⁻ ions. Fe³⁺(aq) + SCN⁻(aq) ⇌ [FeSCN]²⁺(aq) equilibrium 1 Fe³⁺(aq) + 4Cl⁻(aq) ⇌ [FeCl₄]⁻(aq) equilibrium 2 Write the expressions for the stability constants, K_stab, for these two equilibria. Include units in your answers. K_stab1 = ______________ units = ______________ K_stab2 = ______________ units = ______________[3]
7. (c)(ii)An equilibrium can be set up between these two complexes as shown in equilibrium 3. [FeCl₄]⁻(aq) + SCN⁻(aq) ⇌ [FeSCN]²⁺(aq) + 4Cl⁻(aq) equilibrium 3 Write an expression for K_eq3 in terms of K_stab1 and K_stab2. K_eq3 = ______________[1]
8. (c)(iii)The numerical values for these stability constants are shown. K_stab1 = 1.4 x 10² K_stab2 = 8.0 x 10⁻² Calculate the value of K_eq3 stating its units. K_eq3 = ______________ units = ______________[2]

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