A factory can make calcium chloride by two routes.
Route 1 uses the reaction:
CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)\mathrm{CaCO_{3}(s) + 2HCl(aq) \rightarrow CaCl_{2}(aq) + H_{2}O(l) + CO_{2}(g)}CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)
Route 2 uses the reaction:
Ca(OH)2(s)+2HCl(aq)→CaCl2(aq)+2H2O(l)\mathrm{Ca(OH)_{2}(s) + 2HCl(aq) \rightarrow CaCl_{2}(aq) + 2H_{2}O(l)}Ca(OH)2(s)+2HCl(aq)→CaCl2(aq)+2H2O(l)
The relative masses of the products shown in the equations are summarised in the table.
| Quantity | Route 1 | Route 2 |
|---|---|---|
| relative mass of calcium chloride | 111 | 111 |
| combined relative mass of the other products | 62 | 36 |
The atom economy is calculated using:
atom economy=relative mass of desired producttotal relative mass of all products×100 \text{atom economy} = \frac{\text{relative mass of desired product}}{\text{total relative mass of all products}} \times 100 atom economy=total relative mass of all productsrelative mass of desired product×100The table gives operating data for the two routes.
| Feature | Route 1 | Route 2 |
|---|---|---|
| percentage yield | 92% | 79% |
| maximum output of calcium chloride | 84 tonnes per day | 52 tonnes per day |
| use of other products | carbon dioxide and water are not reused | water is fed back into the process |
| cost of producing one tonne of calcium chloride | £360 | £320 |
Calculate the total relative mass of all the products in each route.
Use the atom economy expression and your answers to part (a) to work out the atom economy of each route.
The factory must choose one route for a period when orders for calcium chloride are high. Evaluate the choice it should make.
151 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.