A technician heats 8.0 g of calcium with 6.4 g of oxygen in a reaction vessel. The reaction is allowed to finish.
2Ca+O2→2CaO \mathrm{2Ca + O_2 \rightarrow 2CaO} 2Ca+O2→2CaORelative atomic mass (ArA_rAr): Ca = 40.0 O = 16.0
After the mixture cools, one of these portions can be added.
| Portion | Substance | Mass |
|---|---|---|
| P | calcium | 3.2 g |
| Q | calcium | 8.0 g |
| R | oxygen | 3.2 g |
| S | oxygen | 8.0 g |
Which option gives the portion that should be added so that, after heating again, neither reactant is left?
Portion R: add 3.2 g of oxygen
Portion S: add 8.0 g of oxygen
Portion Q: add 8.0 g of calcium
Portion P: add 3.2 g of calcium
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.