CAIE A-Level Chemistry 28.5.2 Writing Kstab Expressions

Practise translating complex-formation equilibria into Kstab expressions with correct ligand powers and omissions.

Exam points

place complex concentration in the numerator and constituent metal-ion and ligand concentrations below
raise free-ligand concentration to its stoichiometric coefficient in the formation equilibrium
omit liquid water when it is the solvent, including aqua ligands displaced during complex formation

[Maximum number: 1]

Copper is a transition element and has atomic number 29.

The following equilibrium exists between two complex ions of copper in the +2 oxidation state.

\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}+4 \mathrm{Cl}^{-} \rightleftharpoons\left[\mathrm{CuCl}_{4}\right]^{2-}+6 \mathrm{H}_{2} \mathrm{O}

Write the expression for the stability constant, $K_{\text {stab }}$ , for this equilibrium.

K_{\text {stab }}=

$K_{\text {stab }}=\left[\mathrm{CuCl}_{4}{ }^{2-}\right] /\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{ }^{2+}\right][\mathrm{C} /]^{4}$

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28.5.2—Write an expression for a Kstab of a complex question 1