Page 462 - SUBSEC October 2017_Neat

02212020/CAPE/SPEC/MS/2017
- 4 –

CHEMISTRY
UNIT 2 — PAPER 02
MARK SCHEME
KC UK XS

Question 2

S.O.: Module: 2 ---- 7.1, 7.2, 8.1, 8.2, 8.3, 8.5

(a) (i) Length of time a solute remains in the column, before
entering the detector [1 mark] 1

(ii) Mobile phase: The solvent or solvent mixture which

moves over the stationary phase carrying the solutes

with it [1 mark] 1

(iii) Commonly used mobile phase in GLC: nitrogen, helium,
argon. Any two [2 marks]
2

Partitioning [1 mark]
(b)
Substances A-D have different solubilities in the solvent

being used. Based on the differences in their solubilities

the substances have different speeds as they pass through

the column. [2 marks]
3

(i) B [1 mark]
(c) 1
(ii) Approximately 6.8 minutes
0.1 minute [1 mark] 1

(d) A – methanal
B – propane
C – methanol

D – propanoic acid 4

[1 mark each]

Methanol has lowest density
Propane is more volatile than methanol and propanoic acid

Propanoic acid is the heaviest or densest 2
[Any 2]

(e)
 Pack a glass column with a paste of SiO2, CaCO3 or Al2O
3

Ensure there are no air spaces.

3
 Using a Pasteur pipette, place about 5cm of liquid plant

pigment mixture in the column.

 Add the solvent (water) slowly to the mixture ensuring

that the paste is not disturbed.

 Open the tap at the base of the column and collect 5

fractions of equal volumes into separate conical flasks.

 Evaporate contents of flask and analyse via TLC.
[5 marks]