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Examine Fig. 5.26.
(i)
Identify the separation technique marked as ‘S’.
(ii)
Label the apparatus A, B and C.
(iii)
Which of the following mixtures can be separated by the technique identified above? Use the data given in Table 5.5. Mixtures:
- (a) water — acetone
- (b) water — salt
- (c) acetone — alcohol
- (d) sand — salt
- (e) alcohol — chloroform
- (f) alcohol — benzene
| Solvent | Water | Acetone | Alcohol | Chloroform | Benzene |
|---|---|---|---|---|---|
| Temperature (°C) | 100 °C | 56 °C | 78 °C | 61 °C | 80 °C |
Show answer
Part (i)
S is distillation . This is confirmed by Table 5.5 being supplied with the question — it gives boiling points, and the technique that separates on boiling point is distillation.
Part (ii)
| Label | Apparatus | What it does |
|---|---|---|
| A | Distillation flask | The round flask on the left holding the boiling mixture, clamped to the stand, sitting on wire gauze and a tripod over the burner, with a thermometer in its neck |
| B | Water condenser | The slanting double-walled glass tube on the right with two rubber pipes — cold water in through one, out through the other. It cools the vapour back into liquid |
| C | Receiver conical flask | The last flask, in which the distillate drips and collects |
An easy way to remember: left to right, first where it boiled, then where it cooled, then where it collected — and A, B, C run in that same order.
Part (iii)
The rule is that simple distillation needs a gap of at least about 25 °C.
| Mixture | Gap | Possible? |
|---|---|---|
| Water and acetone | 100 − 56 = 44 °C | Yes |
| Water and salt | A liquid with a dissolved solid | Yes |
| Acetone and alcohol | 78 − 56 = 22 °C | No — this needs fractional distillation |
| Sand and salt | Both solids, so boiling point plays no part | No — dissolve in water and filter instead |
| Alcohol and chloroform | 78 − 61 = 17 °C | No — this needs fractional distillation |
| Alcohol and benzene | 80 − 78 = 2 °C | No — this needs fractional distillation |
