A student investigated the reaction between magnesium and dilute hydrochloric acid. The rate of this reaction is directly proportional to the concentration of the acid.
The table shows one of the student's results.
Table: The time taken for the magnesium to react completely at two different concentrations of dilute hydrochloric acid
| Concentration of hydrochloric acid (mol/dm3) | Time for the magnesium to react completely (s) |
|---|---|
| 0.50 | 180 |
| 1.50 | not yet known |
Calculate the time expected for the magnesium to react completely using acid of concentration 1.50 mol/dm3.
The time the student measured using 1.50 mol/dm3 acid was 74 s, which is longer than the time calculated in part a.
Suggest one reason why the measured time was longer.
Explain, in terms of particles, why the rate of this reaction is proportional to the concentration of the acid.
127 exam-style questions on AQA GCSE Chemistry 6.1 Rate of reaction, covering 6.1.1a Calculating rates of reactions, 6.1.1b Gradient of a tangent as rate, 6.1.2 Factors which affect the rates of chemical reactions, 6.1.3 Collision theory and activation energy, and 6.1.4 Catalysts. Each one has a worked solution and a mark scheme showing where the marks go.