(a)[1]
Explain what the term ligand means.
(b)[2]
$\text{Cr}^{3+}(aq)$ and $\text{C}_2\text{O}_4^{2-}(aq)$ ions combine to form the complex ion $[\text{Cr}(\text{C}_2\text{O}_4)_2(\text{H}_2\text{O})_2]^-$. Draw two stereoisomers of this complex ion. You may use a diagram to show $\text{C}_2\text{O}_4^{2-}$.
(c(i))[2]
The solubility of calcium ethanedioate, $\text{CaC}_2\text{O}_4$, is $6.65 \times 10^{-3}\,\text{g dm}^{-3}$ at $298\,\text{K}$. Write an expression for the solubility product, $K_{sp}$, of $\text{CaC}_2\text{O}_4$. State the units.
(c(ii))[2]
Calculate the numerical value of $K_{sp}$ for $\text{CaC}_2\text{O}_4$ at $298\,\text{K}$. Give your answer in standard form to two significant figures.