DP Chemistry (last assessment 2024)

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Question 23M.3.SL.TZ1.6

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Date May 2023 Marks available [Maximum mark: 8] Reference code 23M.3.SL.TZ1.6
Level SL Paper 3 Time zone TZ1
Command term Describe, Determine, Predict, State, Write Question number 6 Adapted from N/A
6.
[Maximum mark: 8]
23M.3.SL.TZ1.6

Lipids and carbohydrates play an essential role in the body.

(a.i)

State the general formula of a carbohydrate.

[1]

Markscheme

Cx(H2O)y ✓

(a.ii)

Fructose is a carbohydrate. Determine the energy, in kJ, released by the respiration of 10.5 g of fructose, C6H12O6.

Enthalpy of (∆Hc⦵) of fructose = −2810 kJ mol−1

[2]

Markscheme

«n=10.5 g/180.18 g mol−1=» 0.0583 «mol» ✓

«0.0583 mol × 2810 kJ mol−1 =» 164 «kJ» ✓


Award [2] for correct final answer.

Award [1 max] for –164 «kJ».

(b)

Lipids and carbohydrates both release energy in the body.

(b.i)

Write balanced equations for the complete oxidation of fructose, C6H12O6, and the triglyceride tristearin, C57H110O6.


C6H12O6: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

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C57H110O6: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

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[2]

Markscheme

C6H12O6 + 6O2 → 6CO2 + 6H2O ✓

C57H110O6 + 81.5O2 → 57CO2 + 55H2O
OR
2C57H110O6 + 163O2 →114CO2 + 110H2O ✓

(b.ii)

Predict, giving one reason, whether 10.5 g of the triglyceride tristearin would release more or less energy than 10.5 g of fructose when completely oxidized.

[1]

Markscheme

more AND contains less oxygen/contains more carbon/more reduced ✓

(c)

Describe the chemical composition of phospholipids and their function in the body, other than as energy storage.


Chemical composition: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

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Function: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

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[2]

Markscheme

Chemical composition:
glycerol AND «two» fatty acids AND «one» phosphate ✓

Function:
cell/plasma membrane ✓


Accept suitable diagram for M1.
Do not accept "hydrophilic head and hydrophobic tail" for M1.

Accept insulation or lipid transport for M2.

Do not accept cell wall for cell membrane.