Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

Compound $R$ is a weak diprotic (dibasic) acid that dissolves very readily in water.
(a(i))

With $\text{H}_2\text{X}$ used to stand for $R$, write a balanced equation for the reaction between $\text{H}_2\text{X}$ and $\text{NaOH}$.

(a(ii))

Use the information above to work out the amount, in moles, of $\text{OH}^-$ ions present in the titration.

(a(iii))

Using your answers to (i) and (ii), determine the amount, in moles, of $R$ in $25.0\,\text{cm}^3$ of solution.

(a(iv))

Calculate the amount, in moles, of $R$ in $250\,\text{cm}^3$ of solution.

(a(v))[5]

Calculate $M_r$ of $R$.

(b(i))

Calculate the $M_r$ of each acid.

(b(ii))[2]

Deduce which of $S$, $T$ or $U$ correctly represents the structure of acid $R$. $R$ is represented by __________.

(c)[5]

State the reagent(s) and essential conditions needed for each of the following conversions.\n\n$S$ into $T$\n\n$S$ into $U$\n\n$T$ into $S$

(d)[2]

Give the structural formula of the organic product formed in each reaction below.\n\n$T$ with an excess of $\text{Na}$\n\n$U$ with an excess of $\text{Na}_2\text{CO}_3$

(e)[2]

Acid $S$ exhibits stereoisomerism. Draw structures to illustrate this isomerism. Label each isomer.

(f)[2]

When one isomer of $S$ is heated at $110\,^\circ\text{C}$ without air, a cyclic compound $V$ with molecular formula $\text{C}_4\text{H}_2\text{O}_3$ is produced. The other isomer of $S$ does not react at this temperature. Suggest the displayed formula of $V$.

Worked solution & mark scheme

This 18-mark question has a full step-by-step worked solution and mark scheme. One marking point: Balanced equation $H_2X + 2NaOH \rightarrow Na_2X + 2H_2O$

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