Crystallisation, sublimation, distillation, extraction and chromatography — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Which purification technique is based mainly on the difference in solubility of a solid in a suitable solvent at different temperatures?

• A. Crystallisation
• B. Sublimation
• C. Simple distillation
• D. Chromatography

Question 2 · difficulty L2 · understanding

Which type of solid is especially suitable for purification by sublimation?

• A. A solid that changes directly from solid to vapour on heating
• B. Any ionic solid with a very high melting point
• C. A solid completely insoluble in every solvent
• D. A solid that decomposes before vaporising

Question 3 · difficulty L2 · understanding

Simple distillation is most suitable for separating

• A. two miscible liquids with very close boiling points
• B. a volatile liquid from non-volatile impurities or liquids with a large boiling-point difference
• C. two solids with different colours
• D. two components solely on the basis of adsorption

Question 4 · difficulty L2 · understanding

In solvent extraction, a solute is transferred preferentially from one liquid phase to another because

• A. the two liquids must react completely
• B. the solute has different solubilities in two usually immiscible solvents
• C. both solvents have identical density
• D. the solute must be a gas

Question 5 · difficulty L3 · application

A mixture contains camphor and common salt. Which method is most appropriate for separating camphor from the salt?

• A. Sublimation
• B. Simple distillation
• C. Chromatography
• D. Fractional crystallisation from water only

Question 6 · difficulty L3 · application

A liquid organic compound contains a small amount of dissolved non-volatile impurity. The compound is stable at its boiling point. Which purification method is most suitable?

• A. Simple distillation
• B. Sublimation
• C. Paper chromatography
• D. Crystallisation

Question 7 · difficulty L3 · application

A coloured mixture gives several spots at different heights on a chromatography plate when developed with a solvent. What is the main reason the components separate?

• A. They have different relative affinities for the stationary and mobile phases
• B. They all have identical solubility and adsorption
• C. Only their molar masses determine the positions
• D. The solvent chemically destroys some components

Question 8 · difficulty L3 · application

An organic compound is much more soluble in ether than in water, while an inorganic salt impurity remains in the aqueous phase. Which technique can separate the organic compound most directly?

• A. Solvent extraction with ether
• B. Sublimation
• C. Simple distillation of the dry salt
• D. Crystallisation without using any solvent

Question 9 · difficulty L4 · application

An impure solid is highly soluble in hot water, sparingly soluble in cold water, and the impurities are insoluble in hot water. Which sequence is best for purification?

• A. Dissolve in minimum hot water, hot-filter, cool to crystallise, then filter the crystals
• B. Add excess cold water, filter immediately, then boil the filtrate to dryness
• C. Sublime the entire mixture and collect every vapour
• D. Distil the solid mixture directly without solvent

Question 10 · difficulty L4 · application

Two miscible liquids have boiling points $78^\circ$C and $82^\circ$C. Which method is more suitable for their separation?

• A. Simple distillation with no fractionating column
• B. Fractional distillation
• C. Sublimation
• D. Solvent extraction using the same two liquids