A student investigates how temperature affects the rate of reaction between sodium thiosulfate solution and dilute hydrochloric acid.
When the two solutions are mixed, a precipitate of sulfur forms slowly, making the mixture turn cloudy. The student places the reaction flask over a sheet of paper with a black cross drawn on it and measures the time taken for the cross to be completely obscured by the precipitate.
The student performs the experiment at five different temperatures. The results are shown in the table below:
| Temperature in ∘C{^\circ}\text{C}∘C | 18 | 24 | 32 | 42 | 58 |
|---|---|---|---|---|---|
| Time taken in seconds | 150 | 110 | 78 | 54 | 30 |
Describe the relationship shown by the results between temperature and the time taken for the cross to be obscured.
Estimate the time taken for the cross to be obscured at 37 ∘C37\ {^\circ}\text{C}37 ∘C.
Explain, in terms of particles, why an increase in temperature increases the rate of this reaction.
State one variable that must be kept constant for the experiment to be valid (a fair test).
14 exam-style questions on Edexcel IGCSE Chemistry Rates of reaction. Each one has a worked solution and a mark scheme showing where the marks go.