Chemistry 9701 · AS & A Level · Carboxylic acids and derivatives
Carboxylic acids and derivatives — practice question
Ethanedioic acid, $\text{C}_2\text{O}_4\text{H}_2$, is found in a range of vegetables. Its amount in spinach may be determined by the following procedure.
• $40.0\,\text{g}$ of spinach leaves are crushed and mixed with distilled water.
• The mixture is filtered, and the leaves are rinsed.
• The combined filtrate and washings are made up to $100.0\,\text{cm}^3$ with water.
• A $25.0\,\text{cm}^3$ portion is transferred to a conical flask with excess dilute sulfuric acid.
• The acidified solution is warmed and titrated with $0.0200\,\text{mol dm}^{-3}$ $\text{KMnO}_4$.
The reaction equation is:
$2\text{MnO}_4^- + 6\text{H}^+ + 5\text{C}_2\text{O}_4^{2-} \rightarrow 2\text{Mn}^{2+} + 10\text{CO}_2 + 8\text{H}_2\text{O}$.
For the titration, $15.20\,\text{cm}^3$ of $\text{KMnO}_4$ was needed.
(a)[3]
Calculate the percentage by mass of ethanedioic acid present in the spinach leaves.
(b(i))[1]
State a suitable reagent for changing ethanedioic acid into ethanedioyl chloride:
$\text{HO}_2\text{CCO}_2\text{H} \rightarrow \text{ClOCCOCl}$.
(b(ii))[2]
For the reactions of ethanedioyl chloride shown, suggest the structures of compounds J and K and place them in the boxes.
(c(i))[2]
Use the Data Booklet to write in the boxes the $\delta$ values for the peaks in the spectrum that are caused by the carbon atoms in ethoxyethane, $\text{CH}_3\text{CH}_2\text{OCH}_2\text{CH}_3$.
(c(ii))[1]
Explain what the rest of the carbon‑13 NMR spectrum tells you about the structure of L.
(d(i))[3]
Suggest the structures of M, N and O.
(d(ii))[1]
Suggest a structure for L that matches all the data given in (c) and (d).
Worked solution & mark scheme
This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: “$n(\mathrm{MnO_4^-}) = \dfrac{0.02 \times 15.2}{1000} = 3.04 \times 10^{-4}\,\mathrm{mol}$” …