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

Carboxylic acids and derivatives — practice question

Aqueous bromine reacts with methanoic acid to produce hydrogen bromide and carbon dioxide gas. $\text{Br}_2(aq) + \text{HCO}_2\text{H}(aq) \rightarrow 2\text{HBr}(aq) + \text{CO}_2(g)$ The table gives the oxidation numbers of bromine and carbon in the species taking part in this reaction.
(a)[1]

Identify the oxidising agent in this reaction. Justify your answer with oxidation numbers.

(b)[1]

Suggest one observation you would make, ignoring any temperature change, when bromine reacts with methanoic acid.

(c(i))[2]

Use the graph to work out the average rate of reaction at $20\,^{\circ}\text{C}$ during the first $600\,\text{s}$. State the units for this rate of reaction.

(c(ii))[1]

Sketch a graph on the same axes to show the expected outcome when the experiment is repeated at $40\,^{\circ}\text{C}$.

(c(iii))[2]

The rate of reaction increases when the number of successful collisions between reactant particles rises. Explain why increasing the temperature produces this effect.

(d)[2]

Complete the ‘dot-and-cross’ diagram, showing outer electrons only, to illustrate the bonding in methanoic acid, $\text{HCO}_2\text{H}$.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: Bromine is oxidised as the oxidation number of Br falls from 0 to $-1$

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