Organic Chemistry
9 marks · HardThis question requires you to use your knowledge of organic functional groups and condensation polymers.
State what is meant by a functional group in organic chemistry and give the functional group present in all alcohols.
Ethane-1,2-diol (a diol) and hexane-1,6-dioic acid (a dicarboxylic acid) can react to form a polyester by condensation polymerisation.
Draw the displayed formula for ethane-1,2-diol.
Draw the displayed formula for hexane-1,6-dioic acid.
Write a balanced chemical equation (using structural formulae) for the formation of the polyester from ethane-1,2-diol and hexane-1,6-dioic acid. Include the structure of one repeat unit (use square brackets with 'n') and water.
Explain why polyesters are generally more biodegradable than addition polymers such as poly(ethene).
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) A functional group is an atom or group of atoms that determines the chemical properties of a compound. The functional group present in all alcohols is the –OH (hydroxyl) group.
(b(i)) Displayed formula for ethane-1,2-diol: · must show Two carbon atoms, each bonded to –OH; four H atoms; all bonds shown
(b(ii)) Displayed formula for hexane-1,6-dioic acid: · must show Six carbon atoms in a chain; carboxylic acid groups (–COOH) at each end; correct hydrogens
(b(iii)) n HOOC–(CH₂)₄–COOH + n HOCH₂CH₂OH → [–OC–(CH₂)₄–COOCH₂CH₂O–]ₙ + 2n H₂O · must show Polyester repeat unit showing ester linkages, Water as by-product, Structural/condensed formula accepted
(c) Polyesters are more biodegradable than addition polymers because they contain ester linkages which can be broken down by hydrolysis (enzymes or acids/bases break the ester bonds). Addition polymers, such as poly(ethene), have only strong carbon–carbon single bonds, which are much less reactive and cannot be easily broken down by microorganisms in the environment. · must show Reason linked to ester group reactivity, Contrast with addition polymers, Reference to biodegradability
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Defines a functional group correctly.
B2 (a) · 1 mark · States –OH (hydroxyl) as the functional group in alcohols.
B3 (b(i)) · 1 mark · Draws displayed formula for ethane-1,2-diol with all atoms and bonds shown.
B4 (b(ii)) · 1 mark · Draws displayed formula for hexane-1,6-dioic acid with six C atoms, both ends as –COOH, all bonds shown.
M1 (b(iii)) · 1 mark · Writes correct balanced structural equation for condensation polymerisation, includes repeat unit in square brackets and water. (follow-through)
A1 (b(iii)) · 1 mark · Shows correct structure of polymer repeat unit: –OC–(CH₂)₄–COOCH₂CH₂O–; brackets, n and water included. (follow-through)
M2 (c) · 1 mark · Explains that ester linkages in polyesters can be broken by hydrolysis or by microorganisms.
M3 (c) · 1 mark · Contrasts with strong carbon–carbon bonds in addition polymers being unreactive/less biodegradable.
A2 (c) · 1 mark · Links explanation to biodegradability in terms of environmental breakdown by hydrolysis.
Worked solution
a) In organic chemistry, a functional group is an atom or group of atoms that determines the characteristic chemical reactions of a compound. The functional group present in all alcohols is the hydroxyl group, written as –OH.
b) i) The displayed formula for ethane-1,2-diol is:
Where each carbon atom is bonded to two hydrogens and one –OH group.
ii) The displayed formula for hexane-1,6-dioic acid is:
This shows a six-carbon chain with a carboxylic acid (–COOH) group on each end.
iii) The balanced equation for the reaction is:
This shows the formation of the polyester with ester links and the by-product water.
c) Polyesters are more biodegradable than addition polymers because they contain ester linkages (–COO–) in the polymer chain. These ester bonds can be hydrolysed (broken) by water, acids, bases, or by enzymes produced by microorganisms, allowing the polymer to break down in the environment. In contrast, addition polymers like poly(ethene) only have strong, non-reactive carbon–carbon bonds in their backbone, which do not break down easily and are not attacked by microorganisms, making them much less biodegradable.