Indigestion tablets contain magnesium hydroxide. Magnesium hydroxide neutralises excess hydrochloric acid in the stomach.
Mg(OH)2(s)+2HCl(aq)→MgCl2(aq)+2H2O(l)\mathrm{Mg(OH)_{2}(s)} + 2\mathrm{HCl(aq)} \rightarrow \mathrm{MgCl_{2}(aq)} + 2\mathrm{H_{2}O(l)}Mg(OH)2(s)+2HCl(aq)→MgCl2(aq)+2H2O(l)
Relative atomic masses: H = 1, O = 16, Mg = 24, Cl = 35.5
A scientist models stomach acid using a solution of hydrochloric acid that contains 7.30 g of hydrogen chloride, HCl, in 500 cm3\mathrm{cm^{3}}cm3 of solution.
Calculate the concentration of this hydrochloric acid in g dm−3\mathrm{g\,dm^{-3}}gdm−3.
Calculate the mass of magnesium hydroxide needed to neutralise exactly 100 cm3\mathrm{cm^{3}}cm3 of this hydrochloric acid.
Each tablet contains 0.580 g of magnesium hydroxide. Determine the number of tablets needed to neutralise the 100 cm3\mathrm{cm^{3}}cm3 of acid.
Calculate the concentration, in g dm−3\mathrm{g\,dm^{-3}}gdm−3, of magnesium chloride in the solution formed when 100 cm3\mathrm{cm^{3}}cm3 of the acid is exactly neutralised. Assume the volume of the solution stays at 100 cm3\mathrm{cm^{3}}cm3.
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.