A student heats aluminium in a crucible so that it reacts with oxygen. After each heating, the crucible is allowed to cool before it is weighed.
| Measurement | Mass / g |
|---|---|
| crucible and lid | 28.40 |
| crucible, lid and aluminium before heating | 28.94 |
| crucible, lid and contents after heating once | 29.34 |
| crucible, lid and contents after heating twice | 29.42 |
| crucible, lid and contents after heating three times | 29.42 |
Relative atomic masses: Al = 27, O = 16
Use the mass data to calculate the simplest whole-number ratio of aluminium atoms to oxygen atoms in the product. Hence state its empirical formula. Show your working.
A student calculates the formula using the mass recorded after the first heating. Explain why their result may not be the same as the result in (a).
142 exam-style questions on Edexcel GCSE Chemistry 2.6 Calculations involving masses, covering 2.6.1 Relative formula mass and percentage composition, 2.6.2 Empirical and molecular formulae, 2.6.3 Conservation of mass, 2.6.4 Reacting masses and concentration in g dm⁻³, 2.6.5 The mole and the Avogadro constant, and 2.6.6 Limiting reactants and stoichiometry. Each one has a worked solution and a mark scheme showing where the marks go.