A student puts some damp iron wool into a sealed gas syringe containing 90 cm3\mathrm{cm^{3}}cm3 of air. After one week, the volume of gas in the syringe has decreased to 72 cm3\mathrm{cm^{3}}cm3, measured at the same temperature and pressure. The iron has rusted by reacting with the oxygen.
Calculate the percentage of oxygen in the air sample.
Assume the iron forms iron(III) oxide.
4Fe(s)+3O2(g)→2Fe2O3(s)\mathrm{4Fe(s)} + \mathrm{3O_{2}(g)} \rightarrow \mathrm{2Fe_{2}O_{3}(s)}4Fe(s)+3O2(g)→2Fe2O3(s)
Calculate the mass of iron that reacted. Relative atomic mass: Fe = 56. One mole of any gas occupies 24 000 cm3\mathrm{cm^{3}}cm3 at room temperature and pressure.
Rusting is an oxidation reaction. Write the half equation for iron atoms forming iron(III) ions.
An underground steel pipeline is protected by connecting it to blocks of magnesium. Explain, in terms of electrons, how the magnesium prevents the iron from rusting.
The student's value for the percentage of oxygen is lower than the true value. Suggest one reason why.
42 exam-style questions on Edexcel GCSE Chemistry 6.1 Transition metals, alloys and corrosion, covering 6.1.1 Properties of transition metals, 6.1.2 Corrosion and its prevention, and 6.1.3 Alloys and the uses of metals. Each one has a worked solution and a mark scheme showing where the marks go.