A student mixes a liquid and a solid in a sealed flask fitted with a closed tap. The reaction produces a gas.
The flask remains on a balance throughout the experiment.
| Measurement | Mass in g |
|---|---|
| Flask and closed tap before the substances are added | 72.54 |
| Liquid added | 18.36 |
| Solid added | 4.25 |
| Flask and contents after the tap is opened and gas escapes | 93.87 |
Calculate the mass of gas that escapes when the tap is opened.
Explain why the balance reading does not change during the reaction while the tap is closed, but decreases when the tap is opened.
95 exam-style questions on AQA GCSE Chemistry 3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations, covering 3.1.1 Conservation of mass and balanced chemical equations, 3.1.2 Relative formula mass, 3.1.3 Mass changes when a reactant or product is a gas, and 3.1.4 Chemical measurements. Each one has a worked solution and a mark scheme showing where the marks go.