Solution X reacts with excess solution Y to form a precipitate.
In the first experiment, a student mixes 20 cm320\,\mathrm{cm^{3}}20cm3 of 0.80 mol/dm30.80\,\mathrm{mol/dm^{3}}0.80mol/dm3 solution X with solution Y.
The student prepares solution X for a second experiment in one of four ways. The temperature and the amount of solution Y are unchanged. Solution Y remains in excess.
| Preparation | Volume of 0.80 mol/dm30.80\,\mathrm{mol/dm^{3}}0.80mol/dm3 solution X in cm3\mathrm{cm^{3}}cm3 | Volume of water added in cm3\mathrm{cm^{3}}cm3 |
|---|---|---|
| P | 20 | 20 |
| Q | 10 | 10 |
| R | 30 | 10 |
| S | 20 | 0 |
The student wants the precipitate to form more slowly at the start, but wants its final mass to be unchanged.
Which preparation should the student use?
Preparation Q: 10 cm310\,\mathrm{cm^{3}}10cm3 of solution X with 10 cm310\,\mathrm{cm^{3}}10cm3 of water
Preparation S: 20 cm320\,\mathrm{cm^{3}}20cm3 of solution X with no added water
Preparation R: 30 cm330\,\mathrm{cm^{3}}30cm3 of solution X with 10 cm310\,\mathrm{cm^{3}}10cm3 of water
Preparation P: 20 cm320\,\mathrm{cm^{3}}20cm3 of solution X with 20 cm320\,\mathrm{cm^{3}}20cm3 of water
122 exam-style questions on OCR GCSE Chemistry 5.2 Controlling reactions, covering 5.2.1 Measuring and interpreting rate of reaction, 5.2.2 Factors affecting rate and collision theory, and 5.2.3 Catalysts, activation energy and enzymes. Each one has a worked solution and a mark scheme showing where the marks go.