Chemistry 9701 · AS & A Level · Group 17

Group 17 — practice question

Potassium chlorate, $\text{KClO}_3$, is used extensively as an oxidising agent and for the preparation of $\text{O}_2$(g).
(a)[1]

Define the term oxidising agent.

(b)[2]

$\text{KClO}_3$(s) decomposes on heating. $\text{MnO}_2$(s) catalyses the exothermic decomposition reaction. Complete and label the diagram in Fig. 3.1 to show how $\text{MnO}_2$(s) affects the decomposition of $\text{KClO}_3$(s).

(c)[1]

If $\text{KClO}_3$ is heated without a catalyst, $\text{KClO}_4$ and $\text{KCl}$ are produced. $4\text{KClO}_3 \rightarrow 3\text{KClO}_4 + \text{KCl}$. Explain why this reaction is called a disproportionation reaction.

(d(i))[1]

Molten $\text{KClO}_3$ reacts with glucose, $\text{C}_6\text{H}_{12}\text{O}_6$. $4\text{KClO}_3 + \text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 4\text{KCl}$. $\text{KClO}_3$ melts at $630\,\text{K}$. At this temperature, both $\text{CO}_2$ and $\text{H}_2\text{O}$ are gases. Use the ideal gas equation to calculate the volume, in $\text{m}^3$, of one mole of gas at $630\,\text{K}$ and $1.00 \times 10^5\,\text{Pa}$. Show your working. Give your answer to 3 significant figures.

(d(ii))[2]

$5.00\,\text{g}$ of $\text{C}_6\text{H}_{12}\text{O}_6$ reacts fully with molten $\text{KClO}_3$. Use your answer to (d)(i) to calculate the total volume of gas produced at $630\,\text{K}$ and $1.00 \times 10^5\,\text{Pa}$ in this reaction.

(e(i))[1]

Fig. 3.2 shows the structure of glucose, $\text{C}_6\text{H}_{12}\text{O}_6$. Complete Table 3.1 by identifying how many primary, secondary and tertiary alcohol groups are present in the structure shown in Fig. 3.2.

(e(ii))[3]

Different samples of aqueous glucose are tested with the reagents listed in Table 3.2. Complete Table 3.2 by giving the observation for each reaction. Write "no reaction" where relevant.

(e(iii))[1]

Many structural isomers exist for $\text{C}_6\text{H}_{12}\text{O}_6$. Define structural isomers.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: A substance that causes another substance to be oxidised and is reduced itself

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