A student makes ammonium sulfate crystals in the laboratory. First the student carries out a titration. 25.0 cm3\mathrm{cm^{3}}cm3 of ammonia solution is pipetted into a conical flask with methyl orange indicator and titrated with 0.100 mol dm−3\mathrm{mol\,dm^{-3}}moldm−3 sulfuric acid.
2NH3(aq)+H2SO4(aq)→(NH4)2SO4(aq)2\mathrm{NH_{3}(aq)} + \mathrm{H_{2}SO_{4}(aq)} \rightarrow \mathrm{(NH_{4})_{2}SO_{4}(aq)}2NH3(aq)+H2SO4(aq)→(NH4)2SO4(aq)
The table shows the student's results.
| Titration | Rough | 1 | 2 | 3 |
|---|---|---|---|---|
| Volume of acid added / cm3\mathrm{cm^{3}}cm3 | 12.90 | 12.45 | 12.55 | 12.50 |
Calculate the mean titre using the concordant results.
Calculate the concentration, in mol dm−3\mathrm{mol\,dm^{-3}}moldm−3, of the ammonia solution.
To make the crystals, the student mixes 250 cm3\mathrm{cm^{3}}cm3 of the ammonia solution with 125 cm3\mathrm{cm^{3}}cm3 of the 0.100 mol dm−3\mathrm{mol\,dm^{-3}}moldm−3 sulfuric acid, without indicator. Calculate the maximum mass of ammonium sulfate that can form. Relative formula mass: (NH4)2SO4=132\mathrm{(NH_{4})_{2}SO_{4}} = 132(NH4)2SO4=132
The student obtains 1.32 g of dry crystals. Calculate the percentage yield.
The student heats the solution to evaporate only some of the water and then leaves it to crystallise, rather than heating it to dryness. Suggest why.
43 exam-style questions on Edexcel GCSE Chemistry 6.3 Dynamic equilibria, covering 6.3.1 The Haber process as a reversible reaction, 6.3.2 Conditions and rate in industrial equilibria, and 6.3.3 Fertilisers and the preparation of ammonium sulfate. Each one has a worked solution and a mark scheme showing where the marks go.