CAIE IGCSE Chemistry 6.2.3 Practical methods for investigating

Practise choosing apparatus and measurements for rate experiments that produce gases or show mass change over time.

Exam points

select gas syringe or mass-loss apparatus for reactions producing H2, O2 or CO2
state measurements needed for rate: gas volume or mass change against time
explain why flask mass decreases when gas escapes from the apparatus

[Maximum number: 3]

Hydrogen peroxide, $\mathrm{H}_{2} \mathrm{O}_{2}$ , decomposes into water and oxygen in the presence of a catalyst, manganese(IV) oxide.

2 \mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{~g})

The student carries out a second experiment to investigate whether another substance, copper(II) oxide, is a better catalyst than manganese(IV) oxide.

Describe how the second experiment is carried out. You should state clearly how you would make sure that the catalyst is the only variable.

same mass / amount of /moles / 1.0 g of catalyst;
same temperature; same volume and concentration of hydrogen peroxide $/ 20 \mathrm{~cm}^{3}$ of $0.1 \mathrm{~mol} / \mathrm{dm}^{3}$ of hydrogen peroxide or reactant;

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6.2.3—Practical methods for investigating question 1