A student mixes an aqueous solution containing 8.50 g of silver nitrate with excess sodium chloride solution. Silver chloride is produced.
AgNO3(aq)+NaCl(aq)→AgCl(s)+NaNO3(aq)\mathrm{AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)}AgNO3(aq)+NaCl(aq)→AgCl(s)+NaNO3(aq)
Relative formula masses (MrM_rMr):
AgNO3=170\mathrm{AgNO_3} = 170AgNO3=170
AgCl=143.5\mathrm{AgCl} = 143.5AgCl=143.5
The student separates the solid product and leaves it to dry. The mass is recorded at intervals.
| Time left to dry in minutes | Mass of solid in g |
|---|---|
| 0 | 7.39 |
| 20 | 6.31 |
| 30 | 6.31 |
Calculate the maximum theoretical mass of silver chloride that could be made from 8.50 g of silver nitrate.
Calculate the percentage yield of dry silver chloride.
The student mistakenly uses 7.39 g as the mass of silver chloride and reports a percentage yield of 103.0%.
Explain why this is not a valid percentage yield.
104 exam-style questions on AQA GCSE Chemistry 3.3 Yield and atom economy of chemical reactions, covering 3.3.1a Percentage yield, 3.3.1b Theoretical mass of a product, 3.3.2a Atom economy, and 3.3.2b Choosing a reaction pathway. Each one has a worked solution and a mark scheme showing where the marks go.