CAIE IGCSE Chemistry 13.2 Experimental Skills and Investigations Topic Practice

Hydrated cobalt(II) sulfate, $\mathrm{CoSO}_{4} \cdot \mathrm{x} \mathrm{H}_{2} \mathrm{O}$, produces water when it is heated.

A student does an experiment to determine the value of x in $\mathrm{CoSO}_{4} \cdot \mathbf{x} \mathrm{H}_{2} \mathrm{O}$.
step 1 The student weighs a sample of hydrated cobalt(II) sulfate.
step 2 The student heats the sample of hydrated cobalt(II) sulfate.
step 3 The student weighs the remaining solid after heating.

Describe what else the student should do to ensure that all the water has been given off. No other substances are required.

Ethanoic acid is a weak acid and hydrochloric acid is a strong acid.
Both ethanoic acid and hydrochloric acid dissociate in aqueous solution.

A student does experiments to show that hydrochloric acid is a strong acid and ethanoic acid is a weak acid. The student adds an excess of hydrochloric acid and an excess of ethanoic acid to separate samples of lumps of calcium carbonate.

Only the identity of the acid is changed between the experiments. All other conditions are kept the same.

The student uses the same size container and checks that the pressure is the same for each experiment.

State three other conditions which must be kept the same to ensure fair testing.
1

2

3

Sulfuric acid is produced by the Contact process. The steps of the Contact process are shown.

Dilute sulfuric acid is a typical acid.

A student adds excess dilute sulfuric acid to a sample of solid copper(II) carbonate in a test-tube.

Give three observations the student would make.

This question is about sodium and compounds of sodium.

A student determines the concentration of a solution of dilute sulfuric acid, $\mathrm{H}_{2} \mathrm{SO}_{4}$, by titration with aqueous sodium hydroxide, NaOH .
step 1 $25.0 \mathrm{~cm}^{3}$ of $0.200 \mathrm{~mol} / \mathrm{dm}^{3} \mathrm{NaOH}$ is transferred into a conical flask.
step 2 Three drops of methyl orange indicator are added to the conical flask.
step 3 A burette is filled with $\mathrm{H}_{2} \mathrm{SO}_{4}$.
step 4 The acid in the burette is added to the conical flask until the indicator changes colour. The volume of acid is recorded. This process is known as titration.
step 5 The titration is repeated several times until a suitable number of results is obtained.

State how the student decides that a suitable number of results have been obtained.