A student heats 1.20 g of magnesium ribbon in a crucible with a lid to make magnesium oxide.
2Mg(s)+O2(g)→2MgO(s)\mathrm{2Mg(s)} + \mathrm{O_{2}(g)} \rightarrow \mathrm{2MgO(s)}2Mg(s)+O2(g)→2MgO(s)
Relative atomic mass: Mg = 24. Relative formula mass: MgO = 40
Show that the theoretical yield of magnesium oxide from 1.20 g of magnesium is 2.00 g.
The student obtains 1.70 g of magnesium oxide. Calculate the percentage yield.
During heating, the student lifts the lid of the crucible from time to time. Explain why the lid must be lifted, and why lifting it too often lowers the yield.
Some of the magnesium reacts with nitrogen in the air to form magnesium nitride. Explain how this affects the percentage yield of magnesium oxide.
51 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.