A student investigates the effect of temperature on the rate of the reaction between sodium thiosulfate solution and dilute hydrochloric acid. The mixture turns cloudy as a solid forms. She places the flask on a cross drawn on paper and times how long it takes for the cross to disappear.
The table shows her results.
| Temperature in °C | Time 1 in s | Time 2 in s | Time 3 in s | Mean time in s |
|---|---|---|---|---|
| 20 | 64 | 66 | 65 | 65 |
| 30 | 33 | 31 | 35 | 33 |
| 40 | 17 | 16 | 27 | ? |
| 50 | 9 | 8 | 10 | 9 |
Give two variables the student must keep the same.
Identify the anomalous result in the table.
Calculate the mean time at 40 °C. Do not include the anomalous result.
The rate of reaction can be found using: rate=1mean time\displaystyle \text{rate} = \frac{1}{\text{mean time}}rate=mean time1
Calculate the rate of reaction at 50 °C. Give your answer to two significant figures.
Describe the effect of increasing temperature on the rate of this reaction.
Different people may see the cross disappear at different times. Suggest one way of improving the method to overcome this problem.
54 exam-style questions on Edexcel GCSE Chemistry 8.1 Rates of reaction, covering 8.1.1 Measuring and interpreting rates of reaction, 8.1.2 Collision theory and the factors affecting rate, and 8.1.3 Catalysts and enzymes. Each one has a worked solution and a mark scheme showing where the marks go.