May/June 2026 Paper 43

Aqueous hydrogen peroxide, H${}_2$O${}_2$, decomposes to produce water and oxygen gas. The reaction is catalysed by manganese(IV) oxide. A student adds powdered manganese(IV) oxide to aqueous hydrogen peroxide in a conical flask as shown in Figure 4.1. The mass of the conical flask and its contents is measured at regular time intervals. The mass decreases as time increases.

State the meaning of the term aqueous.

Complete the symbol equation for the decomposition of aqueous hydrogen peroxide.

State why there is a decrease in mass of the conical flask and its contents during the experiment.

The rate of reaction is highest at the start of the reaction. The rate of reaction decreases as time increases. The rate of reaction eventually becomes zero because the reaction stops. Explain why the rate of reaction decreases as time increases.

The experiment is repeated at a higher temperature. All other conditions remain the same. Explain why the rate of reaction is greater at the higher temperature.

Oxygen is also produced by thermal decomposition of potassium manganate(VII), KMnO${}_4$. State the meaning of (VII) in potassium manganate(VII).

The equation for the reaction is shown.

Calculate the mass of KMnO${}_4$ used to produce 0.64 g of O${}_2$. [$M_{\mathrm{r}}$: KMnO${}_4$, 158; O${}_2$, 32] Use the following steps. • Calculate the number of moles of O${}_2$ produced. • Calculate the number of moles of KMnO${}_4$ used. • Calculate the mass of KMnO${}_4$ used.