A student reacts marble chips with dilute hydrochloric acid in a flask fitted with a cotton wool plug. Carbon dioxide escapes from the flask, and the student records the mass of the flask and its contents over time.
At 40 s, the mass is 186.42 g. A tangent to the mass-time curve at 40 s passes through these points.
| Point on tangent | Time / s | Mass / g\mathrm{g}g |
|---|---|---|
| P | 10 | 186.66 |
| Q | 70 | 186.18 |
Calculate the rate of mass loss at 40 s.
Assume that the rate of mass loss remains constant from 40 s to 55 s. Calculate the estimated mass of the flask and its contents at 55 s.
122 exam-style questions on OCR GCSE Chemistry 5.2 Controlling reactions, covering 5.2.1 Measuring and interpreting rate of reaction, 5.2.2 Factors affecting rate and collision theory, and 5.2.3 Catalysts, activation energy and enzymes. Each one has a worked solution and a mark scheme showing where the marks go.