Tuesday 18 June 2024 – Morning
A Level Chemistry B (Salters)
H433/02 Scientific literacy in chemistry
Time allowed: 2 hours 15 minutes
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, 2
1 Trans fats are made from carboxylic acids with double bonds in a trans arrangement.
They sometimes improve the texture of foods, but they are harmful to health.
(a) Fig. 1.1 shows the structure of a fat molecule.
Fig. 1.1
H 2C O A
HC O O
B
H2C O O
C
O
(i) The side-chains formed by three carboxylic acids are labelled A, B and C.
Give the letter of the side-chain that is:
Saturated ...............
Trans unsaturated ...............
[1]
(ii) The fat molecule in Fig. 1.1 can be represented as shown below.
Complete the equation for the hydrolysis of the fat with aqueous NaOH.
H O
H C O C R'
O
H C O C R''
O
H C O C R'''
H
[3]
(b) Long-chain carboxylic acids can be identified by converting them to their methyl esters and then
using gas–liquid chromatography.
Write the equation for the conversion of RCOOH to its methyl ester using the appropriate alcohol.
, 3
(c) In gas–liquid chromatography, the methyl esters are injected into a stream of carrier gas and
passed through a column containing the stationary phase.
(d) Oils are fats which are liquid at room temperature. Many oils are made from palmitic and stearic
acids, as well as other carboxylic acids.
To identify an oil, the methyl esters of the carboxylic acids, including methyl palmitate and methyl
stearate, are made from the oil.
The oil can be identified from the gas–liquid chromatogram of the methyl esters using the ratio of
methyl palmitate:methyl stearate from the peak heights.
Linseed oil has a methyl palmitate:methyl stearate ratio of 5:4.
Use the gas–liquid chromatograms below to decide which of the oils D, E or F is linseed oil.
Give your reasoning.
Recorder
response
100 100 100 100 100
50 50 50 50 50
0 0 0 0 0
0 10 20 30 0 10 20 30 0 10 20 30 0 10 20 30 0 10 20 30
Time / min Time / min Time / min Time / min Time / min
pure pure oil D oil E oil F
methyl palmitate methyl stearate
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