A student does four experiments to investigate the law of conservation of mass.
Experiment 1: The student heats 2.54 g of copper powder in an open dish. The copper reacts with oxygen in the air. Black copper oxide is made.
Experiment 2: The student adds dilute hydrochloric acid to sodium carbonate solution in an open beaker. The mixture fizzes.
Experiment 3: The student does Experiment 2 again in a sealed plastic bottle.
Experiment 4: The student mixes barium chloride solution with sodium sulfate solution in an open beaker. A white solid forms. There is no fizzing.
The table shows the results.
| Experiment | Mass of container and contents at start (g) | Mass of container and contents at end (g) |
|---|---|---|
| 1 | 32.54 | 33.18 |
| 2 | 185.40 | 184.52 |
| 3 | 186.10 | 186.10 |
| 4 | 162.35 | 162.35 |
Which experiment is done in a closed system?
Balance the equation for the reaction in Experiment 1.
...... Cu + O₂ → ...... CuO
Describe and explain the change in mass, or lack of change in mass, in each experiment.
Use the results and ideas about particles.
55 exam-style questions on OCR GCSE Chemistry 3.1 Introducing chemical reactions, covering 3.1.1 Writing formulae and balanced chemical equations, 3.1.2 Formulae of compounds from ions, and state symbols, 3.1.3 Conservation of mass and observed changes in mass, 3.1.4 Half equations and balanced ionic equations, 3.1.5 The mole and the Avogadro constant, and 3.1.6 Stoichiometry, limiting reactants and reacting masses. Each one has a worked solution and a mark scheme showing where the marks go.