A technician heats mixtures of zinc and sulfur. Zinc sulfide is the only product.
Zn+S→ZnS\mathrm{Zn} + \mathrm{S} \rightarrow \mathrm{ZnS}Zn+S→ZnS
Relative atomic masses: Zn=65\mathrm{Zn}=65Zn=65, S=32\mathrm{S}=32S=32
Each reaction goes to completion, and no product is lost.
| Mixture | Mass of zinc / g\mathrm{g}g | Mass of sulfur / g\mathrm{g}g | Mass of zinc sulfide produced / g\mathrm{g}g |
|---|---|---|---|
| P | 3.25 | 2.40 | 4.85 |
| Q | 4.55 | 1.60 | 4.85 |
Explain why mixtures P and Q produce the same mass of zinc sulfide, although they contain different masses of zinc and sulfur.
A third mixture contains 5.20 g of zinc and 1.92 g of sulfur. Calculate the mass of zinc sulfide produced.
Calculate the mass of zinc left over when the third mixture has reacted.
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.