A pilot plant makes chemical Q by a single reaction. It carries out two trials, each starting with the same quantities of fresh starting materials.
In trial 1, the unreacted starting materials are thrown away after one pass through the reactor.
In trial 2, the unreacted starting materials are separated and passed through the reactor a second time.
| Mass of Q collected | Trial 1 | Trial 2 |
|---|---|---|
| From the first pass (kg) | 450 | 450 |
| From the second pass (kg) | 0 | 180 |
The theoretical yield of Q from the fresh starting materials is 750 kg.
In the balanced equation, Q has a balancing number of 1. The Mr M_r\,Mr of Q is 156, and the sum of the Mr M_r\,Mr values of all the products, each multiplied by its balancing number, is 240.
Calculate the percentage yield of Q in each trial.
Calculate the atom economy for making Q.
Explain why recovering the unreacted starting materials increases the percentage yield but does not change the atom economy.
152 exam-style questions on OCR GCSE Chemistry 5.1 Monitoring chemical reactions, covering 5.1.1 The technique of titration, 5.1.2 Theoretical mass, percentage yield and atom economy, 5.1.3 Concentration of a solution in mol/dm3, 5.1.4 Concentration calculations and titration results, 5.1.5 Molar gas volume and volumes of gases in reactions, and 5.1.6 Choosing a reaction pathway. Each one has a worked solution and a mark scheme showing where the marks go.