| Statement | True / False | Corrected statement, where needed |
|---|---|---|
| (i) Salt can be separated from a salt solution by evaporation or distillation. | True | — |
| (ii) Distillation can be used for separation of two liquids even when these have the same boiling point. | False | Distillation can separate two miscible liquids only when their boiling points differ by at least about 25 °C. |
| (iii) In paper chromatography, the solvent level should be above the sample spot at the beginning of the experiment. | False | The solvent level should be below the sample spot at the beginning of the experiment. |
| (iv) Evaporation and crystallization are the same processes. | False | They are different: evaporation removes the solvent to leave the solute behind, while crystallization deposits a pure solid as regular crystals from a saturated solution. |
(i) Why it is true. Salt is a non-volatile solid: it does not vaporise at the temperatures involved. So if the water is driven off — either by evaporating it into the air or by boiling it off and condensing it in a distillation set-up — the salt is left behind in the vessel in both cases. Distillation does more: it also gives you back the pure water.
(ii) Why it is false. Distillation depends on one liquid vaporising before the other. If two liquids boil at the same temperature they vaporise together, and the distillate has the same composition as the mixture — nothing is separated.
(iii) Why it is false. If the solvent level starts above the spot, the ink is simply washed off into the solvent in the jar and lost. The whole method depends on the solvent rising through the paper and reaching the spot from below, so the level must start below the spot.
(iv) Why it is false.
| Point | Evaporation | Crystallization |
|---|---|---|
| What is removed | The solvent is driven off | The solvent stays; the excess solute comes out |
| What drives it | Heating or exposure to air | Slow cooling of a hot saturated solution |
| Purity of the product | All dissolved impurities are left behind with the solute | Impurities remain in the liquid; the crystals are pure |
| Form of the solid | A crust or fine powder | Well-shaped crystals with regular geometry |