Chemistry 9701 · AS & A Level · Group 17

Group 17 — practice question

Potassium chlorate, KClO$_3$, is commonly employed as an oxidising agent and for the preparation of O$_2$(g).
(a)[1]

Define oxidising agent.

(b)[2]

KClO$_3$(s) decomposes on heating. MnO$_2$(s) acts as a catalyst for the exothermic decomposition reaction. Finish and label the diagram in Fig. 3.1 to show how MnO$_2$(s) affects the decomposition of KClO$_3$(s).

(c)[1]

When KClO$_3$ is heated without a catalyst, KClO$_4$ and 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 KClO$_3$ reacts with glucose, C$_6$H$_{12}$O$_6$. $4\text{KClO}_3 + \text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 4\text{KCl}$. KClO$_3$ melts at $630\,\text{K}$. At this temperature, both CO$_2$ and H$_2$O are gases. Use the ideal gas equation to work out 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 method. Give your answer to 3 significant figures.

(d(ii))[2]

5.00 g of C$_6$H$_{12}$O$_6$ reacts completely with molten 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]

The structure of glucose, C$_6$H$_{12}$O$_6$, is shown in Fig. 3.2. Complete Table 3.1 to identify how many primary, secondary and tertiary alcohol groups are present in the structure shown in Fig. 3.2.

(e(ii))[3]

Separate samples of aqueous glucose are tested with the reagents shown in Table 3.2. Complete Table 3.2 with the observation for each reaction. Write "no reaction" where that is appropriate.

(e(iii))[1]

There are many structural isomers of C$_6$H$_{12}$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: Definition of oxidising agent: a substance that oxidises another substance and is itself reduced

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