A solid compound, X, decomposes when it is heated in an open boiling tube. The only products are a solid, Y, and a gas, which escapes from the tube.
A student carries out two experiments.
| Experiment | Heating outcome | Starting mass of X (g) | Mass of solid in the tube after heating (g) |
|---|---|---|---|
| 1 | X decomposes completely | 12.0 | 7.5 |
| 2 | Heating is stopped before all of X decomposes | 20.0 | 14.6 |
Calculate the mass of X that remains in the tube at the end of experiment 2.
The student continues heating the solid from experiment 2 until all the remaining X has decomposed.
Calculate the decrease in the mass of solid during this further heating.
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.