Edexcel IGCSE Chemistry Standard-form Numbers

Practise Edexcel IGCSE Chemistry standard-form numbers by calculating reaction rate from time and converting the value to standard form.

Exam points

Calculate a reaction rate from one divided by time and convert the decimal to standard form.

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

All question bank results loaded

1B Standard-form numbers question 1