IB Questionbank

User interface language: English | Español

Date	May 2017	Marks available	2	Reference code	17M.3.hl.TZ1.25
Level	HL	Paper	3	Time zone	TZ1
Command term	Suggest	Question number	25	Adapted from	N/A

Question

Solubility plays an important role in the bioavailability of drugs in the body.

Suggest why aspirin is slightly soluble in water. Refer to section 37 of the data booklet.

[2]

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.

[2]

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.

[2]

Some mild analgesics contain a solid mixture of acidic aspirin and a non-acidic organic chemical of similar polarity to asprin.

Discuss how acid-base properties and the process of solvent extraction can be used to separate aspirin from the mixture.

[3]

The pharmaceutical industry is one of the largest producers of waste solvents.

State a green solution to the problem of organic solvent waste.

[1]

Markscheme

presence of «large» benzene/arene ring AND non-polar/hydrophobic
OR
presence of «large» benzene/arene ring AND cannot form H-bond with water

contain COOH/carboxyl/–OH/hydroxyl «and ester group» AND polar/hydrophilic
OR
contain COOH/carboxyl/–OH/hydroxyl «and ester group» AND can form H-bonds with water

Accept “phenyl” for “benzene ring”.

Accept "carboxylic acid" for "carboxyl".

Do not accept "alcohol" for "hydroxyl".

[2 marks]

«student’s» sample impure

lattice disrupted/not uniform «due to presence of impurities»
OR
fewer interparticle/intermolecular forces «due to presence of impurities»

Accept converse arguments.

[2 marks]

One similarity:
peak at 2500–3000 «cm^–1»/peak due to O–H/hydroxyl in carboxylic acids
OR
peak at 1700–1750 «cm^–1»/peak due to C=O/carbonyl
OR
peak at 2850–3090 «cm^–1»/peak due to C–H of arene

One difference:
peak at 3200–3600 «cm^–1» in salicylic acid/ peak due to O–H in phenol in salicylic acid
OR
«two» peaks at 1700–1750 «cm^–1» in aspirin AND one peak «in the same area» in salicylic acid

Accept “peak at 1600 cm^–1 for arene/benzene ring” – not in the data booklet.

Accept “2500–3600 cm^–1 «overlapping absorptions of two O–H» in salicylic acid”.

Accept “stronger/broader/split peak at 1700–1750 cm^–1 in aspirin”.

[2 marks]

dissolve compounds in an organic solvent

add NaOH(aq)/OH^–(aq) «to the mixture» to convert aspirin to its water soluble salt

separate the two «immiscible» layers

convert salt «in aqueous layer» back to aspirin by reacting with acid/H⁺

«evaporate solvents and dry»

Accept organic solvents immiscible with water such as hexane, ethyl ethanoate, butyl acetate.

Accept any other base.

Need explanation for mark.

[3 marks]

«use of» alternative solvents such as supercritical/liquid CO₂
OR
use of water «as solvent»
OR
solvent-free reactions «for example, polymerization of propene»
OR
solid-state chemistry
OR
recycle «waste» solvents
OR
catalysis that leads to better/higher yield
OR
reducing number of steps