A water-recovery unit distils used rinse water containing dissolved salts. Water vapour passes from the boiling flask through a side arm into a condenser.
The thermometer bulb is tested in two positions in separate trials.
| Position | Position of thermometer bulb | Steady reading |
|---|---|---|
| P | Below the surface of the rinse water | 103 °C |
| Q | Level with the side arm | 100 °C |
The technician needs to measure the boiling point of the distillate being collected.
Explain which thermometer position should be used.
The technician collects the distillate and evaporates a 10 cm³ sample.
| Measurement | Result |
|---|---|
| Mass of empty evaporating basin | 61.42 g |
| Mass of basin and residue after evaporation | 61.43 g |
Evaluate the claim that the distillate is close to pure water.
Use the thermometer reading from the correct position and a calculation in your answer.
87 exam-style questions on AQA GCSE Chemistry 10.1 Using the Earth's resources and obtaining potable water, covering 10.1.1 Using the Earth's resources and sustainable development, 10.1.2 Potable water, 10.1.3 Waste water treatment, and 10.1.4 Alternative methods of extracting metals. Each one has a worked solution and a mark scheme showing where the marks go.