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Date	November 2016	Marks available	1	Reference code	16N.3.sl.TZ0.18
Level	SL	Paper	3	Time zone	TZ0
Command term	State	Question number	18	Adapted from	N/A

Question

The mild analgesic aspirin can be prepared in the laboratory from salicylic acid.

(CH₃CO)₂O + HOC₆H₄COOH → CH₃CO₂C₆H₄COOH + CH₃COOH

Salicylic acid Aspirin

After the reaction is complete, the product is isolated, recrystallized, tested for purity and the experimental yield is measured. A student’s results in a single trial are as follows.

Literature melting point data: aspirin = 138–140 °C

Determine the percentage experimental yield of the product after recrystallization. The molar masses are as follows: M(salicylic acid) = 138.13 g mol⁻¹, M(aspirin) = 180.17 g mol⁻¹. (You do not need to process the uncertainties in the calculation.)

[2]

Suggest why isolation of the crude product involved the addition of ice-cold water.

[1]

Justify the conclusion that recrystallization increased the purity of the product, by reference to two differences between the melting point data of the crude and recrystallized products.

[2]

State why aspirin is described as a mild analgesic with reference to its site of action.

[1]

Markscheme

ALTERNATIVE 1:
«theoretical yield = $\frac{{1.552\,{\text{g}}}}{{138.13\,{\text{g}}\,{\text{mo}}{{\text{l}}^{ - 1}}}}$ × 180.17 g mol⁻¹ =» 2.024 «g»

«experimental yield = $\frac{{1.124{\rm{g}}}}{{2.024{\rm{g}}}}$ × 100 =» 55.53 «%»

ALTERNATIVE 2:
« $\frac{{1.552\,{\text{g}}}}{{138.13\,{\text{g}}\,{\text{mo}}{{\text{l}}^{ - 1}}}}$ »= 0.01124 «mol salicylic acid/aspirin theoretical» AND

« $\frac{{1.124\,{\text{g}}}}{{180.17\,{\text{g}}\,{\text{mo}}{{\text{l}}^{ - 1}}}}$ »= 0.006239 «mol aspirin experimental»

«experimental yield = $\frac{{0.006239{\rm{mol}}}}{{0.01124{\rm{mol}}}}$ x 100 =» 55.51 «%»

Accept answers in the range 55.4 % to 55.7 %.
Award [2] for correct final answer.

low temperature gives greater difference between solubility of aspirin and impurities
OR
«product» crystallizes out from cold solution/«ice-cold water/lower temperature» speeds up crystallization process
OR
aspirin/product has low solubility «in water» at low temperatures

[N/A]

intercepts pain stimulus at source/acts at site of pain
OR
interferes with production of pain sensitizing substances/prostaglandins «at site of pain»

Examiners report

[N/A]

recrystallized melting point is higher
OR
recrystallized melting point is closer to pure substance/literature value

smaller range of values

[N/A]

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.
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.
20N.3.sl.TZ0.11a:
Deduce the structural formula of the by-product of this reaction.
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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