Edexcel IGCSE Chemistry Accuracy and Validity

Practise Edexcel IGCSE Chemistry accuracy and validity by explaining gas loss, timing errors and changes that improve practical measurements.

Exam points

Explain how stirring or measuring both solution temperatures improves temperature accuracy.
Identify gas loss from late syringe connection as a reason for lower measured gas volume.
Suggest timing or reading errors that could cause anomalous practical results.

[Maximum number: 1]

A student investigates the effect of temperature on the rate of reaction between two solutions, A and B . When the reaction occurs, the mixture turns from colourless to blue.

This is the student's method.
- pour $25 \mathrm{~cm}^{3}$ of solution A into a conical flask
- add solution B and measure the temperature of the mixture
- record the time taken for the mixture to turn blue

The student repeats this method at different temperatures.

The table shows the student's results.

Table for Question Evaluate accuracy and validity question 1 — Edexcel IGCSE Chemistry

Give a reason for the anomalous result.

Any one from

M1 temperature was higher than $25^{\circ} \mathrm{C}$

M2 started the timer too late / stopped the timer too early/took reading too early

ALLOW ecf from
incorrect anomalous
result circled so

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Evaluate accuracy and validity question 1