Yield, purity and atom economy sim
Make calcium carbonate and weigh it to constant mass, find the purity of marble from the carbon dioxide lost, see why a yield is low or impossibly high, and compare routes by atom economy.
Chemical calculations: percentage yield, percentage purity and atom economy · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Percentage yield compares what you made with the most you could make: the actual mass divided by the theoretical mass, times 100. The theoretical mass comes from the limiting reactant, the one that runs out first. Here, calcium chloride and sodium carbonate solutions (both 0.500 mol/dm³) react 1 : 1 to make calcium carbonate, Mr 100: CaCl₂(aq) + Na₂CO₃(aq) → CaCO₃(s) + 2NaCl(aq). The yield is below 100 % when solid is lost (splashing, leaving solid in the beaker, a torn filter paper); it can come out above 100 %, which is impossible for the pure, dry product, when the solid is weighed before it is dry, or is not washed, so dissolved sodium chloride dries onto it. That is why you dry and weigh again until two readings agree (constant mass). Percentage purity: marble chips react with excess hydrochloric acid, CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂, and the carbon dioxide escapes, so the mass on the balance falls. The mass lost is the carbon dioxide; times 100 and divided by 44 it gives the calcium carbonate; that divided by the mass of the sample, times 100, is the purity. Atom economy (AQA): the total Mr of the wanted product divided by the total Mr of all the reactants, times 100. Model limits: the losses and the drying rate are illustrative; a careful run still loses 2 %; the impurities in the marble do not react. In a real purity run, carbon dioxide that stays dissolved makes the purity slightly low, water vapour escaping with the gas makes it slightly high (the cotton wool reduces this), and any other carbonate in the impurities would also give off carbon dioxide. The balance reads to 0.01 g.
- Measuring cylinders: 0.500 mol/dm³ solutions
- Balance pan: reads to 0.01 g
- Oven at 110 °C: dry, weigh, repeat to constant mass
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