DP Chemistry (last assessment 2024)

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Question 18M.3.sl.TZ1.7b

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Date May 2018 Marks available [Maximum mark: 3] Reference code 18M.3.sl.TZ1.7b
Level sl Paper 3 Time zone TZ1
Command term Explain Question number b Adapted from N/A
b.
[Maximum mark: 3]
18M.3.sl.TZ1.7b

Saturated lipids found in butter and unsaturated lipids found in fish oil readily become rancid.

(b)

Butter contains varying proportions of oleic, myristic, palmitic and stearic acids. Explain in terms of their structures why stearic acid has a higher melting point than oleic acid, using section 34 of the data booklet.

[3]

Markscheme

«stearic acid» straight chain/chain has no kinks/more regular structure

OR

«stearic acid» saturated/no «carbon–carbon» double bonds

 

«stearic acid» chains pack more closely together

stronger London/dispersion/instantaneous induced dipole-induced dipole forces «between molecules»

 

Accept “«stearic acid» greater surface area/electron density”.

[3 marks]

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