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Date May 2019 Marks available 1 Reference code 19M.3.hl.TZ2.22
Level HL Paper 3 Time zone TZ2
Command term Determine Question number 22 Adapted from N/A

Question

A student synthesized aspirin, acetylsalicylic acid, in a school laboratory.

0.300 g of crude aspirin was dissolved in ethanol and titrated with sodium hydroxide solution, NaOH (aq).

NaOH (aq) + C9H8O4 (in ethanol) → NaC9H7O4 (aq) + H2O (l)

Predict one absorption band present in an infrared (IR) spectrum of aspirin, using section 26 of the data booklet.

[1]
a.

Determine the mass of aspirin which reacted with 16.25 cm3 of 0.100 mol dm−3 NaOH solution.

[2]
b(i).

Determine the percentage purity of the synthesized aspirin.

[1]
b(ii).

Outline how aspirin can be chemically modified to increase its solubility in water.

[1]
c.

State why aspirin should not be taken with alcohol.

[1]
d.

Markscheme

Any one of:
1050–1410 «cm1 due to C–O»  [✔]
17001750 «cm1 due to C=O in acids and esters» [✔]
25003000 «cm1 due to O–H in acids» [✔]
28503090 «cm1 due to C–H in alkanes and arenes» [✔]

a.

n(aspirin) «= n(NaOH) =  16.25  c m 3 1000 × 0.100 mol dm–3 »= 1.625 × 10–3 «mol»  [✔]

m(aspirin) «= 1.625 × 10–3 mol × 180.17 g mol–1 »= 0.293 «g»  [✔]

 

Note: Award [2] for correct final answer.

b(i).

«  0.293  g 0 .300 g × 100 % »= 97.7 «%»  [✔]

b(ii).

convert to a salt
OR
react with sodium hydroxide  [✔]

 

Note: Accept other reactions forming soluble salts.

Accept “to ionize” but not “more polar”.

c.

synergistic effect/increased toxicity
OR
increased risk of stomach/intestines bleeding/ulcers/heartburn
OR
increased risk of liver toxicity/damage
OR
increased risk of nausea/vomiting   [✔]

d.

Examiners report

This was a very well answered question. Even weak candidates were able to identify one correct absorption band present in an infrared spectrum of aspirin.

a.

A significant number of candidates were able to calculate the mass of aspirin correctly.

b(i).

A significant number of candidates were able to calculate the percentage purity of aspirin correctly although some managed an ECF mark.

b(ii).

This part was reasonably answered by most candidates.

c.

This part was well answered by the majority of the candidates.

d.

Syllabus sections

Options » D: Medicinal chemistry » D.2 Aspirin and penicillin
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