An aqueous solution of cobalt(II) chloride is a pink colour due to the presence of [Co(H₂O)₆]²⁺ complex ions.

1. (a)(i)Complete Table 6.1 to describe what is observed when the named reagent is added to an aqueous solution of cobalt(II) chloride. Table 6.1 reagent | colour of cobalt-containing product | state of cobalt-containing product NaOH(aq) | | an excess of conc. HCl | | [2][2]
2. (a)(ii)Write an equation for the reaction between [Co(H₂O)₆]²⁺ ions and NaOH(aq). [1][1]
3. (a)(iii)Write an equation for the reaction between [Co(H₂O)₆]²⁺ ions and an excess of conc. HCl. [1][1]
4. (b)(i)Define stability constant. [1][1]
5. (b)(ii)Write an expression for the stability constant, Kstab, of the [Co(NH₃)₆]²⁺ complex ion. Kstab = ......................................................................................................................................... [1][1]
6. (b)(iii)Give the units of the stability constant, Kstab, of the [Co(NH₃)₆]²⁺ complex ion. units = .............................................. [1][1]
7. (b)(iv)The numerical value of the stability constant, Kstab, of the [Co(NH₃)₆]²⁺ complex ion is 7.7 × 10⁴. In an aqueous solution the concentration of the [Co(NH₃)₆]²⁺ complex ion is 0.0740 mol dm⁻³ and the concentration of NH₃ is 0.480 mol dm⁻³ at equilibrium. Calculate the concentration of [Co(H₂O)₆]²⁺ in this solution. concentration = .............................................. mol dm⁻³ [1][1]

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