Methods Of Purification

Question 1

This is one of the most commonly used techniques for the purification of solid organic compounds

Answer 1

Crystallisation

Question 2

…………….. based on the difference in the solubilities of the compound and the impurities in a suitable solvent

Answer 2

Crystallisation

Question 3

The impure compound is dissolved in a solvent in which it is sparingly soluble at……. temperature but appreciably soluble at……. temperature.

Answer 3

room

higher

Question 4

If the compound is highly soluble in one solvent and very little soluble in another solvent……….. can be satisfactorily carried out in a mixture of these solvents.

Answer 4

crystallisation

Question 5

Impurities, which impart colour to the solution are removed by adsorbing over………..

Answer 5

activated charcoal

Question 6

Crystallisation can be used for purification of…..

Answer 6

Sugar
Potash alum

Question 7

…………….. is used to separate sublimable compounds from non-sublimable impurities.

Answer 7

Sublimation

Question 8

Sublimation can be used for purification of……..(4)

Answer 8

Iodine
Naphthalene
Camphor
Ammonium chloride

Question 9

Distillation is based on principle of difference in………….. of components of mixtures

Answer 9

Boiling point

Question 10

……………. can be used to separate volatile liquids from nonvolatile impurities

Answer 10

Distillation

Question 11

4 types of distillation methods

Answer 11

Simple distillation: boiling point difference >20
Fractional distillation: boiling point difference <20
Vacuum distillation (distillation under reduced pressure): boiling point difference >20 but decomposed at or below boiling point
Steam distillation: dissolve in vapour

Question 12

Simple distillation

Answer 12

For sufficient boiling point difference
For chloroform (bp=334K) and aniline (bp=457K)

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Question 13

Fractional distillation

Answer 13

For those with low difference of boiling point
The vapours of such liquids are formed within the same temperature range and are condensed simultaneously
The vapours of a liquid mixture are passed through a fractionating column before condensation
The fractionating column is fitted over the mouth of the round bottom flask
Vapours of the liquid with higher boiling point condense before the vapours of the liquid with lower boiling point
Is used to separate different fractions of crude oil in petroleum industry.

Question 14

Each successive condensation and vaporisation unit in the fractionating column is called a………..

Answer 14

theoretical plate

Question 15

Distillation under reduced pressure

Answer 15

This method is used to purify liquids having very high boiling points and those, which decompose at or below their boiling points
Such liquids are made to boil at a temperature lower than their normal boiling points by reducing the pressure on their surface.
Glycerol can be separated from spent-lye in soap industry by using this technique.

Question 16

Steam Distillation

Answer 16

This technique is applied to separate substances which are steam volatile and are immiscible with water.
The mixture of steam and the volatile organic compound is condensed and collected
The liquid boils when the sum of vapour pressures due to the organic liquid (p1) and that due to water (p2) becomes equal to the atmospheric pressure (p), i.e. p =p1+ p2.
p1 is lower than p, the organic liquid vaporises at lower temperature than its boiling point.
Separation of aniline,nitrobenzene,ortho nitro phenol from their respective mixture with water

Question 17

If one of the substances in the mixture is water and the other, a water insoluble substance, then the mixture will boil close to but below…….

Answer 17

373K

Question 18

When an organic compound is present in an aqueous medium, it is separated by shaking it with an organic solvent in which it is more soluble than in water. This is called as

Answer 18

Differential Extraction

Question 19

Statement 1: The organic solvent and the aqueous solution should be immiscible with each other so that they form two distinct layers which can be separated by separatory funnel
Statement 2: If the organic compound is less soluble in the organic solvent, a very large quantity of solvent would be required to extract even a very small quantity of the compound

Answer 19

Both are correct regarding differential extraction

Question 20

Statement 1: In chromatography the mixture of substances is applied onto a stationary phase, which is always a solid.
Statement 2: A pure solvent, a mixture of solvents, or a gas is allowed to move slowly over the stationary phase

Answer 20

Statement 1 is incorrect and 2 is correct
Stationary phase can be solid or liquid

Question 21

The moving phase is called the mobile phase it is composed of (3) different things

Answer 21

A pure solvent, a mixture of solvents, or a gas

Question 22

………………. Chromatography is based on the fact that different compounds are adsorbed on an adsorbent (silica gel/alumina) to different degrees.

Answer 22

Adsorption
When a mobile phase is allowed to move over a stationary phase (adsorbent), the components of the mixture move by varying distances over the stationary phase

Question 23

……….. chromatography involves separation of a mixture over a column of adsorbent (stationary phase) packed in a glass tube

Answer 23

Column

Question 24

Component of mixture which is more soluble in stationary phase is adsorbed first than the component which is less soluble in stationary phase in column chromatography

Answer 24

True

Question 25

In column chromatography the most readily adsorbed substances are retained near the top and others come down to various distances in the column

Answer 25

True

Question 26

………… chromatography which involves separation of substances of a mixture over a thin layer of an adsorbent coated on glass plate

Answer 26

Thin layer (TLC)

Question 27

TLC is based on which phenomenon

Answer 27

Capillary action

Question 28

A thin layer about…….. thick of an adsorbent (silica gel or alumina) is spread over a glass plate of suitable size.

Answer 28

0.2mm

Question 29

The plate is known as thin layer chromatography plate or……...

Answer 29

chromaplate

Question 30

The solution of the mixture to be separated is applied as a small spot about……….cm above one end of the TLC plate

Answer 30

2 cm

Question 31

As the eluant rises up the plate, the components of the mixture move up along with the eluant to different distances depending on their ………..and separation takes place.

Answer 31

degree of adsorption

Question 32

The relative adsorption of each component of the mixture is expressed in terms of its retardation factor i.e. Rf value

Answer 32

Rf= ratio of distances moved by substance from base line to that of solvent from base line

Question 33

Spots of compounds, which adsorb iodine, will show up as……… spots.

Answer 33

brown

Question 34

Amino acids may be detected by spraying the plate with…….. solution

Answer 34

ninhydrin

Question 35

………….. chromatography is based on continuous differential partitioning of components of a mixture between stationary and mobile phases.

Answer 35

Partition

Question 36

………… chromatography is a type of partition chromatography.

Answer 36

Paper

Question 37

In……. chromatography, a special quality paper known as chromatography paper is used

Answer 37

paper

Question 38

Chromatography paper contains…….. trapped in it, which acts as the stationary phase.

Answer 38

water

Question 39

The paper selectively retains different components according to their differing partition in the two phases.

Answer 39

True

Question 40

The paper strip so developed is known as a……...

Answer 40

chromatogram