Ethanedioate ions, $\text{C}_2\text{O}_4^{2-}$, act as bidentate ligands. Explain what the term ligand means.
$\text{Cr}^{3+}(aq)$ and $\text{C}_2\text{O}_4^{2-}(aq)$ ions combine to give 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. A simplified structure may be used to show $\text{C}_2\text{O}_4^{2-}$.
At $298\,\text{K}$, the solubility of calcium ethanedioate, $\text{CaC}_2\text{O}_4$, is $6.65 \times 10^{-3}\,\text{g dm}^{-3}$. Write the solubility product expression, $K_{sp}$, for $\text{CaC}_2\text{O}_4$, and include its units.
Calculate the numerical value of $K_{sp}$ for $\text{CaC}_2\text{O}_4$ at $298\,\text{K}$. Present your answer in standard form to two significant figures.