A technician heats iron wool in open crucibles. In each experiment, the iron combines with oxygen to form the same iron oxide, and no solid escapes.
| Experiment | Mass of iron before heating (g) | Mass of solid after heating (g) |
|---|---|---|
| Heated until all the iron reacts | 5.58 | 7.98 |
| Heating stopped while some iron remains | 13.95 | 17.55 |
What mass of iron has reacted in the experiment where heating was stopped while some iron remained?
5.58 g
12.0 g
3.60 g
8.37 g
134 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.