If a sample of hydrated lithium ethanedioate, $\text{Li}_2\text{C}_2\text{O}_4 \cdot \text{H}_2\text{O}$, is heated gently, two gases are produced and a white solid residue is left. The residue is then added to HNO$_3$(aq). A gas is given off that makes limewater turn milky. Complete the equation for the decomposition of $\text{Li}_2\text{C}_2\text{O}_4 \cdot \text{H}_2\text{O}$. $\text{Li}_2\text{C}_2\text{O}_4 \cdot \text{H}_2\text{O} \rightarrow \ldots + \ldots + \ldots$
The pattern in the decomposition temperatures of the Group 2 ethanedioates is the same as that for the Group 2 nitrates. Suggest which of CaC$_2$O$_4$ and BaC$_2$O$_4$ decomposes at the lower temperature. Explain your answer.
Potassium iron(III) ethanedioate, $\text{K}_3\left[\text{Fe(C}_2\text{O}_4)_3\right]$, forms a green solution when it dissolves in water. Explain why transition elements are able to form coloured complexes.
On heating, the anhydrous iron(III) compound $\text{K}_3\left[\text{Fe(C}_2\text{O}_4)_3\right]$ breaks down to give a mixture of $\text{K}_2\left[\text{Fe(C}_2\text{O}_4)_2\right]$, K$_2$C$_2$O$_4$ and CO$_2$. Complete the equation for the decomposition of $\text{K}_3\left[\text{Fe(C}_2\text{O}_4)_3\right]$.
The complex ion $[\text{Fe}(\text{C}_2\text{O}_4)_3]^{3-}$ exhibits stereoisomerism. Finish the three-dimensional diagrams in Fig. 3.1 so that they show the two stereoisomers of $[\text{Fe}(\text{C}_2\text{O}_4)_3]^{3-}$. The $\text{C}_2\text{O}_4^{2-}$ ligand may be represented by $\mathrm{O} \!\!\frown\!\! \mathrm{O}$.
Buffer solutions are used to control pH. Write two equations to show how a solution containing $\text{HC}_2\text{O}_4^{-}$ ions acts as a buffer when small quantities of acid or alkali are added.
A fuel cell is an electrochemical cell that can be used to produce electrical energy by using oxygen to oxidise a fuel. Ethanedioic acid, $(\text{COOH})_2$, dissolved in an alkaline electrolyte is being investigated as a fuel. The relevant standard electrode potentials, $E^{\ominus}$, for the cell are shown. $\text{O}_2(\text{g}) + 2\text{H}_2\text{O}(\ell) + 4\text{e}^- \rightleftharpoons 4\text{OH}^-(\text{aq}) \quad E^{\ominus} = +0.40\,\text{V}$ $2\text{CO}_2(\text{g}) + 2\text{e}^- \rightleftharpoons \text{C}_2\text{O}_4^{2-}(\text{aq}) \quad E^{\ominus} = -0.59\,\text{V}$ Use these equations to work out the overall cell reaction. Calculate the value of $E^{\ominus}_{\text{cell}}$.