Erwin Smith > Purification > Flashcards

Purification Flashcards

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1
Q

What is chromatography?

A

Technique used to separate components of a mixture based on distribution between stationary and mobile phases

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2
Q

What is chromatogram?

A

The developed paper or plate showing separated components

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3
Q

What are the two main types of chromatography?

A

Adsorption chromatography and partition chromatography

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4
Q

What is stationary phase?

A

Phase that remains fixed during chromatography

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5
Q

What is mobile phase?

A

Phase that moves over stationary phase

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6
Q

Principle of chromatography

A

Difference in adsorption or partition of components

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7
Q

What is adsorption chromatography?

A

Separation based on different adsorption
of components on a solid adsorbent

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8
Q

Stationary phase in adsorption chromatography

A

Solid adsorbent

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9
Q

Common adsorbents in adsorption chromatography

A

Silica gel and alumina

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10
Q

Relation between adsorption and mobility

A

Adsorption is inversely proportional to mobility

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11
Q

Types of adsorption chromatography

A

Column chromatography and thin layer chromatography

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12
Q

What is thin layer chromatography (TLC)?

A

Separation on a thin layer of adsorbent coated on glass plate

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13
Q

Thickness of TLC layer

A

About 0.2 mm

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14
Q

Common adsorbent in TLC

A

Silica gel or alumina

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15
Q

What is chromatoplate?

A

Glass plate coated with adsorbent used in TLC

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16
Q

Where is sample applied in TLC?

A

As a small spot above the base line

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17
Q

What is solvent front?

A

Maximum distance travelled by solvent

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18
Q

Formula of Rf value

A

Rf = distance moved by substance / distance moved by solvent

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19
Q

Rf value depends on what?

A

Nature of solute solvent and adsorbent

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20
Q

Relation between polarity and Rf value

A

More polar substance has lower Rf value

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21
Q

Relation between adsorption and Rf value

A

Rf is inversely proportional to adsorption power

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22
Q

How are coloured compounds detected in TLC?

A

By direct observation

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23
Q

How are colourless compounds detected in TLC?

A

By UV light or iodine vapours

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24
Q

Reagent used to detect amino acids in TLC

A

Ninhydrin solution

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25
Colour of iodine vapour spot
Brown
26
What is partition chromatography?
Separation based on differential partition between two liquid phases
27
Stationary phase in paper chromatography
Water trapped in cellulose fibres
28
Mobile phase in paper chromatography
Organic solvent
29
Paper chromatography is a type of which chromatography?
Partition chromatography
30
Material of chromatography paper
Cellulose
31
What is purification?
Removal of impurities from substances
32
Main purification methods
Sublimation crystallisation distillation extraction chromatography
33
What is sublimation?
Direct conversion of solid to vapour without liquid state
34
Principle of sublimation
Only sublimable substance vaporises
35
Used to separate which substances by sublimation?
Sublimable solids from non-sublimable impurities
36
Example of sublimable substance
Naphthalene
37
What is crystallisation?
Purification of solids based on solubility difference
38
Condition for solvent in crystallisation
High solubility at high temperature and low at room temperature
39
Why solution is concentrated in crystallisation?
To obtain nearly saturated solution
40
What happens on cooling during crystallisation?
Pure compound crystallises out
41
How are coloured impurities removed in crystallisation?
By adsorption over activated charcoal
42
Examples of crystallisation
Benzoic acid naphthalene
43
What is distillation?
Separation based on difference in boiling points
44
Principle of distillation
Vaporisation followed by condensation
45
When is simple distillation used?
Large difference in boiling points
46
Example of simple distillation
Chloroform and aniline
47
When is fractional distillation used?
Small difference in boiling points
48
What is fractionating column?
Column providing repeated condensation and vaporisation
49
Industrial example of fractional distillation
Crude oil separation
50
What is vacuum distillation?
Distillation under reduced pressure
51
Why vacuum distillation is used?
To distil high boiling liq or low bp decomposing liquids
52
Example of vacuum distillation
Glycerol from spent lye
53
What is steam distillation?
Distillation using steam
54
Used for which compounds in steam distillation?
Steam volatile and water-immiscible compounds
55
Example of steam distillation
Aniline from aniline-water mixture
56
What is differential extraction?
Separation based on solubility difference in two immiscible solvents
57
Instrument used in extraction
Separating funnel
58
When is continuous extraction used?
When solubility in organic solvent is low
59
What is column chromatography?
Adsorption chromatography using a vertical column
60
Stationary phase in column chromatography
Silica gel or alumina
61
Mobile phase in column chromatography
Solvent
62
Which compound elutes first in column chromatography?
Least adsorbed compound
63
Relation between adsorption and elution
More adsorbed moves slower
64
Mobility order corresponds to what?
Inverse of adsorption power
65
More adsorption means what?
Less mobility
66
Rf is inversely proportional to what?
Adsorption and polarity
67
Silica gel is polar or non-polar?
Polar
68
Partition chromatography uses which phases?
Liquid-liquid
69
Rf proportionality with distance substance, adsorb, eluant, polarity, mobility
Rf proportionality relations Rf ∝ distance travelled by substance; Rf ∝ mobility; Rf ∝ eluant polarity; Rf ∝ 1/adsorption strength; Rf ∝ 1/adsorbent polarity
Erwin Smith
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