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Date	November 2020	Marks available	1	Reference code	20N.3.sl.TZ0.11
Level	SL	Paper	3	Time zone	TZ0
Command term	Deduce	Question number	11	Adapted from	N/A

Question

Aspirin is formed by reacting salicylic acid with ethanoic anhydride. The structure of aspirin is given in section 37 of the data booklet.

Deduce the structural formula of the by-product of this reaction.

[1]

Aspirin crystals are rinsed with water after recrystallization to remove impurities.
Suggest why cold water is used.

[1]

The solubility of aspirin is increased by converting it to an ionic form. Draw the structure of the ionic form of aspirin.

[1]

Comment on the risk of overdose when taking aspirin as an analgesic, referring to the following values, for a person weighing $70 kg$ :

Minimum therapeutic dose $= 0.5 g$

Estimated minimum lethal dose $= 15 g$

[1]

Markscheme

${CH}_{3} COOH$ ✔

Accept full OR condensed structural formula.

to avoid dissolving the crystals/aspirin ✔

Accept “to avoid loss of product” OR “aspirin is less soluble in cold water”.

✔

Accept a positive metal ion next to the $C O O^{-}$ such as “ $N a^{+} / K^{+}$ ”.

Accept “ $- O N a / - O K$ ” without showing the charges.

Accept notations such as “ $R C O O^{-}$ ” OR “ $R C O O N a$ ” OR “ $R C O O K$ ” but not “ $R O^{-}$ ” OR “ $R O N a$ ” OR “ $R O K$ ”.

low/medium risk «of overdosing» AND «estimated» lethal dose is $30$ times/much larger than therapeutic dose

$30$ times the dose results in chance of dying ✔

Accept “ $30$ and low/medium risk due to large therapeutic index”.
Do not accept “low/medium risk AND large therapeutic window”.
Do not accept “ $30$ times the dose” alone for the mark.

Examiners report

A well answered question. Most candidates chose to enter the full structure. Some incorrect answers gave the aspirin product or the salicylic acid rather than the acetic acid.

While there were many good answers it was worrying to correct as many where the student clearly didn't establish a connection between solubility and purification. Many incorrect responses indicated the cold water was to "stay below the melting point of the aspirin" rather than relate it to the solubility of the final product.

Not well answered. Students evidenced familiarity with the content but failed to provide correct structures. Showing lines used to represent covalent bonds to show an ionic interaction, using convention for complexes, showing only one ion were some of the many mistakes. Many students also had an incorrect product having the aspirin lose the -OH group from the carboxylic acid or the entire carboxylic acid functional group rather than just the H⁺.

This is a topic that continues to challenge students and "low/medium risk AND large therapeutic window" was worryingly common. There were also many students who did not calculate the ratio correctly.

Syllabus sections

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

Show 65 related questions

18M.3.sl.TZ1.13c.iv:
State how penicillins may be modified to increase their effectiveness.
18M.3.sl.TZ2.16a.ii:
State how penicillins may be modified to increase their effectiveness.
17N.3.hl.TZ0.22b: Describe how mild analgesics function.
17N.3.sl.TZ0.17a: Aspirin is a mild analgesic derived from salicylic acid found in willow bark. Describe how...
17M.3.sl.TZ2.15b.i:
State how aspirin can be converted to water-soluble aspirin.
16N.3.sl.TZ0.18d: State why aspirin is described as a mild analgesic with reference to its site of action.
17M.3.sl.TZ1.19c:
A student prepares aspirin from salicylic acid in the laboratory, extracts it from the reaction mixture, ensures the sample is dry and determines its melting point.

Suggest why the melting point of the student’s sample is lower and not sharp compared to that of pure aspirin.
17M.3.hl.TZ1.25c:
Organic molecules can be characterized using infrared (IR) spectroscopy.

Compare and contrast the infrared peaks above 1500 cm⁻¹ in pure samples of aspirin and salicylic acid using section 26 of the data booklet.
19M.3.sl.TZ2.15a:
Predict one absorption band present in an infrared (IR) spectrum of aspirin, using section 26 of the data booklet.
18N.3.sl.TZ0.12a: State the internal bond angles in the β-lactam ring and the expected bond angles for the same...
18N.3.sl.TZ0.12d: State how the structure of penicillin can be changed to combat this effect.
18N.3.sl.TZ0.12e: Suggest why human cells are not affected by penicillin.
18N.3.hl.TZ0.16d: Suggest why human cells are not affected by penicillin.
18N.3.hl.TZ0.16a: State the internal bond angles in the b-lactam ring and the expected bond angles in sp2 and...
18N.3.hl.TZ0.16c: State how the structure of penicillin can be modified to combat the effect of...
18N.3.hl.TZ0.16b: Explain how the open β-lactam ring kills bacteria.
18N.3.sl.TZ0.12b: Explain how the open β-lactam ring kills bacteria.
17M.3.hl.TZ1.25b:
A student prepares aspirin from salicylic acid in the laboratory, extracts it from the reaction mixture, ensures the sample is dry and determines its melting point.

Suggest why the melting point of the student’s sample is lower and not sharp compared to that of pure aspirin.
18M.3.sl.TZ2.16c:
Explain why aspirin is not stored in a hot, humid location.
17N.3.sl.TZ0.21: Molecules of antibiotics often contain a beta-lactam ring. Explain the importance of the...
19M.3.sl.TZ1.15b(i):
The widespread use of penicillin and its derivatives has led to the appearance of resistant S. aureus strains.

Outline how these bacteria inactivate the antibiotics.
19M.3.sl.TZ1.15b(ii):
Outline how the structure of penicillin has been modified to overcome this resistance.
16N.3.sl.TZ0.16a:
(i) Outline what is meant by the term “ring strain”.

(ii) On the diagram above, label with asterisk/s (*) the carbon atom/s that experience ring strain.
17M.3.sl.TZ1.19b:
Formulate an equation for the conversion of aspirin to a more water soluble derivative.
19M.3.sl.TZ2.15d:
State why aspirin should not be taken with alcohol.
19M.3.sl.TZ1.15a:
Identify the feature in penicillin responsible for its antibiotic activity.
17M.3.hl.TZ2.20a.iv:
State two techniques, other than IR spectroscopy, which could be used to confirm the identity of aspirin.
18M.3.sl.TZ1.13c.i:
Compare and contrast the IR spectrum of aspirin with that of salicylic acid, using section 26 of the data booklet.
19N.3.hl.TZ0.25a: Explain how the beta-lactam ring is responsible for the antibiotic properties of penicillin....
18M.3.sl.TZ2.16a.i:
Describe how penicillin combats bacterial infections.
19N.3.sl.TZ0.17a: Suggest one reactant used to prepare aspirin from salicylic acid.
19M.3.sl.TZ2.15b(ii):
Determine the percentage purity of the synthesized aspirin.
17M.3.sl.TZ1.19d:
Organic molecules can be characterized using infrared (IR) spectroscopy.

Compare and contrast the infrared peaks above 1500 cm⁻¹ in pure samples of aspirin and salicylic acid using section 26 of the data booklet.
19M.3.hl.TZ1.19a:
Unreacted salicylic acid may be present as an impurity in aspirin and can be detected in the infrared (IR) spectrum.

Name the functional group and identify the absorption band that diff erentiates salicylic acid from aspirin. Use section 26 of the data booklet.

Name:

Absorption band:
19M.3.sl.TZ1.14:
Aspirin can be obtained from salicylic acid.

Unreacted salicylic acid may be present as an impurity in aspirin and can be detected in the infrared (IR) spectrum.

Name the functional group and identify the absorption band that differentiates salicylic acid from aspirin. Use section 26 of the data booklet.

Name:

Absorption band:
18M.3.sl.TZ1.13b.ii:
Outline how the bioavailability of aspirin may be increased.
17M.3.hl.TZ1.25a:
Suggest why aspirin is slightly soluble in water. Refer to section 37 of the data booklet.
17M.3.sl.TZ2.15a.iii:
State two techniques which could be used to confirm the identity of aspirin.
19N.3.sl.TZ0.18c: The discovery of penicillins contributed to the development of antibiotics. Explain how the...
19M.3.hl.TZ1.20b(i):
The widespread use of penicillin and its derivatives has led to the appearance of resistant S. aureus strains.

Outline how these bacteria inactivate the antibiotics.
18M.3.sl.TZ2.16b:
State the type of reaction used to synthesize aspirin from salicylic acid.
19M.3.hl.TZ2.22d:
State why aspirin should not be taken with alcohol.
19M.3.hl.TZ2.22b(ii):
Determine the percentage purity of the synthesized aspirin.
19M.3.hl.TZ2.22c:
Outline how aspirin can be chemically modified to increase its solubility in water.
19M.3.hl.TZ1.20b(ii):
Outline how the structure of penicillin has been modified to overcome this resistance.
19M.3.sl.TZ2.15b(i):
Determine the mass of aspirin which reacted with 16.25 cm³ of 0.100 mol dm⁻³ NaOH solution.
19M.3.hl.TZ1.20a:
Identify the feature in penicillin responsible for its antibiotic activity.
18M.3.sl.TZ1.13c.ii:
Describe how penicillin combats bacterial infections.
19M.3.hl.TZ2.22b(i):
Determine the mass of aspirin which reacted with 16.25 cm³ of 0.100 mol dm⁻³ NaOH solution.
18M.3.sl.TZ1.13a:
Aspirin is often taken to reduce pain, swelling or fever. State one other use of aspirin.
19M.3.hl.TZ2.22a:
Predict one absorption band present in an infrared (IR) spectrum of aspirin, using section 26 of the data booklet.
19N.3.sl.TZ0.17b:
Aspirin, C₆H₄(OCOCH₃)COOH, is only slightly soluble in water.

Outline, including an equation, how aspirin can be made more water-soluble. Use section 37 in the data booklet.
16N.3.sl.TZ0.16b:
(i) Some antibiotic-resistant bacteria produce a beta-lactamase enzyme which destroys penicillin activity. Suggest how adding clavulanic acid to penicillin enables the antibiotic to retain its activity.

(ii) Populations of antibiotic-resistant bacteria have increased significantly over the last 60 years. Outline why antibiotics such as penicillin should not be prescribed to people suffering from a viral infection.
19M.3.sl.TZ2.15c:
Outline how aspirin can be chemically modified to increase its solubility in water.
20N.3.hl.TZ0.15b: Aspirin crystals are rinsed with water after recrystallization to remove impurities.Suggest...
20N.3.hl.TZ0.15c:
The solubility of aspirin is increased by converting it to an ionic form. Draw the structure of the ionic form of aspirin.
17M.3.sl.TZ1.19a:
Suggest why aspirin is slightly soluble in water. Refer to section 37 of the data booklet.
20N.3.sl.TZ0.11b: Aspirin crystals are rinsed with water after recrystallization to remove impurities.Suggest...
20N.3.hl.TZ0.15a:
Deduce the structural formula of the by-product of this reaction.
20N.3.hl.TZ0.19b(ii):
Explain, with reference to the action of penicillin, why new penicillins with different side-chains need to be produced.
20N.3.hl.TZ0.15e:
Explain how IR spectroscopy can be used to distinguish aspirin from salicylic acid.
20N.3.sl.TZ0.14b(i): Circle the side-chain in penicillin on the structure below.
20N.3.sl.TZ0.14b(ii):
Explain, with reference to the action of penicillin, why new penicillins with different side-chains need to be produced.
20N.3.hl.TZ0.19b(i): Circle the side-chain in penicillin on the structure below.
20N.3.sl.TZ0.11c:
The solubility of aspirin is increased by converting it to an ionic form. Draw the structure of the ionic form of aspirin.

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Options » D: Medicinal chemistry

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