Ni²⁺ ions form a number of different complex ions, including [Ni(H₂O)₆]²⁺, [Ni(NH₃)₆]²⁺ and [Ni(en)₃]²⁺. The abbreviation en represents 1,2-diaminoethane. The numerical values of two stability constants, Kstab, are given in Table 5.1. Table 5.1 complex Kstab [Ni(NH₃)₆]²⁺ 4.8 x 10⁷ [Ni(en)₃]²⁺ 2.0 x 10¹⁸

1. (a)Complete the expression for the Kstab of [Ni(en)₃]²⁺. Kstab =[1]
2. (b)(i)A solution of [Ni(H₂O)₆]²⁺ is added to a solution that contains 0.10moldm⁻³ NH₃ and 0.10 mol dm⁻³ en. Predict which complex ion, [Ni(NH₃)₆]²⁺ or [Ni(en)₃]²⁺, is present in the resulting mixture in the highest concentration. Explain your answer. complex ion present in largest concentration = explanation[1]
3. (b)(ii)Complete the equation for the ligand exchange reaction occurring in (i). [Ni(H₂O)₆]²⁺ +[1]
4. (c)Complete Fig. 5.1 to show the three-dimensional structures of the two isomers of [Ni(en)₃]²⁺. Use N N to represent the en ligand. Name the type of isomerism shown. [Figure 5.1] type of isomerism shown[3]

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