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NEET Chemistry · Purification and Characterisation of Organic Compounds

Purification: crystallisation, distillation, extraction, chromatography

Taught in NCERT Class 11 Chemistry, Chapter 8: Organic Chemistry: Some Basic Principles and Techniques.

2 verified questions: Easy 1 · Medium 1 · NEET level 0

Sample questions

Sample 1Easy

In the soap industry, glycerol is separated from spent-lye by

  1. A

    steam distillation

  2. B

    fractional distillation

  3. C

    simple distillation

  4. D

    distillation under reduced pressure

Show the answer
The answer is D.

Liquids that decompose at or below their boiling points are purified by distillation under reduced pressure, which lowers the boiling point. Glycerol is separated from spent-lye in the soap industry by this method.

  • A.

    Steam distillation is used for steam-volatile substances immiscible with water, such as aniline.

  • B.

    Fractional distillation separates liquids with close boiling points, such as crude oil fractions.

  • C.

    Glycerol decomposes near its boiling point, so simple distillation at normal pressure is unsuitable.

NCERT: Class 11 Chemistry, Unit 8 (Organic Chemistry: Some Basic Principles and Techniques), Methods of Purification of Organic Compounds: Distillation under reduced pressure

Sample 2Medium

A thin-layer chromatography plate is drawn: a glass plate coated with silica gel, with a pencil base line 1.0 cm from the bottom carrying a spot of a mixture, developed in a solvent. After development the solvent front is 8.0 cm above the base line, and one component's spot is 3.2 cm above the base line. What is the retardation factor Rf of this component?

  1. A

    0.40

  2. B

    2.5

  3. C

    0.47

  4. D

    0.36

Show the answer
The answer is A.

Rf = distance moved by the substance from the base line ÷ distance moved by the solvent front from the base line = 3.2 cm/8.0 cm = 0.40.

  • B.

    This divides the solvent distance by the spot distance; Rf is the distance moved by the substance over that moved by the solvent.

  • C.

    This measures both distances from the bottom edge of the plate instead of from the base line (4.2/9.0).

  • D.

    This adds 1.0 cm to the solvent distance only; both distances must be measured from the base line.

NCERT: Class 11 Chemistry, Chapter 8

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