CAIE IGCSE Chemistry 13.2.4 Interpret and Evaluate Experimental Data Questions

Work through a real CAIE IGCSE Chemistry question deciding when repeated measurements are sufficiently close to use.

Exam points

evaluate repeat results and decide that sufficient concordant data have been obtained when at least two results agree within an appropriate tolerance

[Maximum number: 1]

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 $125.0 \mathrm{~cm}^{3}$ 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.

at least two results are within $0.2 \mathrm{~cm}^{3}$ or less

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CAIE IGCSE Chemistry 13.2.4 Interpret and Evaluate Experimental Data Questions question 1