Chemistry 9701 · AS & A Level · Carboxylic acids and derivatives

Carboxylic acids and derivatives — practice question

The four isomeric esters below, each with molecular formula $\text{C}_7\text{H}_{14}\text{O}_2$, are employed as synthetic flavourings in drinks and sweets to give foodstuffs a pear, banana or plum flavour.
(a(i))

In each space below, enter one or more of the letters A-D, as needed. Which of these compounds can exist as optical isomers?

(a(ii))[3]

On hydrolysis, which of these compounds yield(s) a secondary alcohol?

(b)[1]

Ethanoic acid, $\text{CH}_3\text{CO}_2\text{H}$, is one of the products formed when all of these compounds undergo hydrolysis. State the reagents and conditions required for this hydrolysis.

(c(i))

The acid dissociation constant, $K_a$, of ethanoic acid is $1.75 \times 10^{-5}\ \text{mol dm}^{-3}$. Explain why this value of $K_a$ is much larger than that of ethanol, $\text{CH}_3\text{CH}_2\text{OH}$, and smaller than that of chloroethanoic acid, $\text{ClCH}_2\text{CO}_2\text{H}$.

(c(ii))[4]

Calculate the pH of a $0.100\ \text{mol dm}^{-3}$ solution of ethanoic acid.

(d(i))

$20.0\ \text{cm}^3$ of $0.100\ \text{mol dm}^{-3}$ NaOH were gradually added to a $10.0\ \text{cm}^3$ sample of $0.100\ \text{mol dm}^{-3}$ ethanoic acid, while the pH was recorded throughout the addition. Calculate the number of moles of NaOH remaining at the end of the addition.

(d(ii))

Calculate the $[\text{OH}^-]$ at the end of the addition.

(d(iii))

Using $K_w = [\text{H}^+][\text{OH}^-]$ and your value from (ii), calculate $[\text{H}^+]$ and the pH of the solution at the end of the addition.

(d(iv))

On the axes below, sketch the way in which pH changes as a total of $20.0\ \text{cm}^3$ of $0.100\ \text{mol dm}^{-3}$ NaOH is added. Make sure the end point is clearly indicated.

(d(v))[7]

From the list of indicators below, place a tick in the box beside the one you judge to be most suitable for this titration.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: The correct answers are B and D

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