Edexcel IGCSE Chemistry Arithmetic Skills

Practise Edexcel IGCSE Chemistry arithmetic and numerical computation by calculating reaction rate and writing the answer in standard form.

Exam points

Calculate mean rate as one divided by time and express the value in standard form.

Covered syllabus points

1A Decimal-form numbers 1B Standard-form numbers 1C Ratios, fractions, percentages, powers and roots

[Maximum number: 2]

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.

Use information from the table to calculate the mean rate of reaction at $20^{\circ} \mathrm{C}$ .

Use the expression

\text { mean rate }=\frac{1}{\text { time in seconds }}

Give your answer in standard form.
mean rate =

M1 $\frac{1}{156}$ OR 0.00641

M2 $\quad 6.41 \times 10^{-3}$

ALLOW use of value from graph

ALLOW $6.4 \times 10^{-3}$

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Covered syllabus points

1 Arithmetic and numerical computation question 1