A sample containing only hydrogen and helium has a total volume of 80 cm380\,\mathrm{cm^{3}}80cm3. The sample is mixed with 50 cm350\,\mathrm{cm^{3}}50cm3 of oxygen. Helium does not react.
A spark causes the hydrogen to react with the oxygen:
2H2(g)+O2(g)→2H2O(l)\mathrm{2H_{2}(g) + O_{2}(g) \rightarrow 2H_{2}O(l)}2H2(g)+O2(g)→2H2O(l)
After the mixture has cooled to room temperature and pressure, the total volume of gas is 70 cm370\,\mathrm{cm^{3}}70cm3.
All gas volumes are measured at the same temperature and pressure.
Calculate the initial volume of hydrogen and the initial volume of helium in the sample.
151 exam-style questions on Edexcel GCSE Chemistry 6.2 Quantitative analysis, covering 6.2.1 Concentration in mol dm⁻³ and titration calculations, 6.2.2 Percentage yield and why actual yield falls short, 6.2.3 Atom economy of a reaction, 6.2.4 Choosing a reaction pathway, and 6.2.5 Molar volume of gases and Avogadro's law. Each one has a worked solution and a mark scheme showing where the marks go.