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C33.1 Chromatography AQA A2 Chemistry C33 Chromatography Kerboodle Answers : Page No. 245
1 In column chromatography the eluent is a liquid. In gas-liquid chromatography it is a gas.
2
IL can separate and help 10 identify minute traces of substances. For example (among others) substances used in making explosives. [Many other suggestions are also acceptable.]
3 a A
b C
c A
d C
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Practice Questions: Page No. 246-247
1 Wearing plastic gloves to hold a TLC plate, draw a pencil line I. 5 cm from the bottom of the plate.
- Use a capillary tube to apply a very small drop of the solution of amino acids to the mid-point of the pencil line.
- Allow the spot to dry completely.
- In the developing tank, add the developing solvent to a depth of not more than I cm.
- Place your TLC plate in the developing tank and seal the tank with a lid.
- Allow the developing solvent to rise up the plate to at least of its height.
- Remove the plate and quickly mark the position of the solvent front with a pencil.
- (a)
Essential – to prevent contamination from thehands to the plate
Add developing solvent to a depth of not more than 1cm3:
Essential – if the solvent is too deep it will dissolve the mixture from the plate
Allow the solvent to rise up the plate to the top:
Not essential – the R
f value can be calculated if the solvent front does not reach the top of the plate
Essential – the solvent is toxic
(b) Spray with developing agent or use UV
Measure distances from initial pencil line to the spots (x)
Measure distance from initial pencil line to solvent front line (y)
R
f value = x / y
(c) Amino acids have different polarities
Therefore, have different retention on the stationary phase or different solubility in the developing solvent
2
(a) The R
fvalues are :
Spot 1: 0.9/5.5 = 0.16 arginine
Spot 2: 2.2/5.5 = 0.40 alanine
Spot 3: 4.0/5.5 = 0.73 arginine
(b) R
f values differ in different solvents
3
(a)
A spot of the mixture to be separated is placed in the corner of a square of chromatography paper, about 1 cm from each edge.
The plate is placed in a chromatography tank containing solvent 1 to a depth of less than 1 cm.
The solvent is allowed to run up the plate and when it nearly reaches the top, the position of the solvent (the solvent front) is marked and the position of any separated spots identified (by using
UV light or a chemical which produces a colour change) and marked.
The plate is then rotated through 900 so that the separated spots are now along the bottom of the plate and the procedure repeated with solvent 2.
(b) Each component has two R
f values both of which must match with a known component.
(c) (i) 23/44 = 0.52
(ii) 22/44 = 0.50
4
- Oxidation (of alcohol by oxygen in air)
- Absorption at 1680–1750 (due to C=O)
- Comparison of polarity of molecules or correct imf statement:
- Propanone is less polar OR propan-2-ol is more polar
- OR Propanone has dipole-dipole forces
- OR Propan-2-ol has hydrogen bonding
- About attraction to stationary phase or solubility in moving phase
- Propan-2-ol has greater affinity for stationary phase or vice versa
- OR Propanone is more soluble in solvent/moving phase or vice versa
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References:
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AQA GCSE Science Kerboodle textbook
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