Show — 3 marks
A manufacturer produces biodegradable packaging from polyhydroxyalkanoates (PHAs), a type of polyester. These polymers are made from renewable resources and can be broken down by microorganisms in soil. The company wants to compare the properties of PHAs with those of traditional polymers and ethanol-based coatings used in packaging applications.
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(a) PHAs are condensation polymers made from hydroxy acids. Show that a hydroxy acid contains both a carboxylic acid group and a hydroxyl group.
[1 mark]
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(b) Show the equation for the condensation polymerisation of a hydroxy acid, using the general formula R-CH(OH)-COOH for the monomer.
[1 mark]
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(c) The manufacturer also uses ethanol as a solvent in some coating formulations. Show why ethanol is a more effective solvent than water for dissolving some non-polar polymeric compounds, by referring to the intermolecular forces involved.
[1 mark]
Show mark scheme
- (a) A hydroxy acid contains both a -COOH (carboxylic acid/carboxyl) group AND a -OH (hydroxyl) group in the same molecule
- (b) Correct condensation polymerisation equation showing: n R-CH(OH)-COOH → [-CO-CH(R)-O-]n + n H2O (or equivalent showing ester linkage formation and water elimination)
- (c) Ethanol contains non-polar C-H bonds / can form induced dipole-induced dipole forces (or van der Waals forces) with non-polar polymers, whereas water forms strong hydrogen bonds and is too polar to dissolve non-polar substances effectively
Define — 2 marks
Plastic bottles used for storing drinks are often made from polymers such as polyethylene terephthalate (PET). These materials are chosen because they are durable and can be recycled. Understanding the structure and properties of polymers helps manufacturers design better packaging materials.
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(a) Define the term 'polymer'.
[1 mark]
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(b) Define the term 'monomer'.
[1 mark]
Show mark scheme
- (a) A large molecule made up of many smaller units (or molecules) joined together / A long chain of atoms covalently bonded together
- (b) A small molecule that can join to other monomers to form a polymer / A simple molecule that is the basic unit of a polymer
Explain — 3 marks
A chemical company manufactures poly(ethene) plastic film used for food packaging. The poly(ethene) is made by polymerising ethene gas in the presence of a catalyst. Ethene is an unsaturated hydrocarbon obtained by cracking crude oil fractions.
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(a) Explain what happens to the double bond in each ethene molecule when poly(ethene) is formed.
[1 mark]
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(b) Explain why the polymerisation of ethene is described as an addition reaction.
[2 marks]
Show mark scheme
- (a) The double bond breaks / opens up (to form single bonds)
- (b) Many monomers / ethene molecules join together to form one polymer / long chain
- (b) No other product is formed / all atoms in the monomer are present in the polymer
Describe — 2 marks
A chemical company manufactures polyethene by heating ethene gas under high pressure. The polyethene produced is used to make plastic bottles and food packaging.
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(a) Describe what happens to ethene molecules when polyethene is formed.
[1 mark]
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(b) Describe one property of polyethene that makes it suitable for making food packaging.
[1 mark]
Show mark scheme
- (a) Many ethene molecules / monomers join together to form long chains / a polymer (accept: double bonds break / open up to form single bonds)
- (b) Any one from: flexible / strong / lightweight / waterproof / unreactive / non-toxic / can be moulded into shape
Evaluate — 3 marks
A packaging company is choosing between two materials for food containers. Poly(lactic acid) (PLA) is a biodegradable polymer made from plant starch through fermentation to produce lactic acid, which is then polymerised. Poly(ethene) is produced from crude oil through fractional distillation and cracking to make ethene, which is then polymerised. The company wants to evaluate which material is more suitable.
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(a) State one advantage and one disadvantage of using PLA instead of poly(ethene) for food packaging.
[2 marks]
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(b) Evaluate whether the company should choose PLA or poly(ethene) for food containers. Give a reason for your answer.
[1 mark]
Show mark scheme
- (a) Advantage: PLA is biodegradable / breaks down naturally / renewable resource used / less landfill waste (1)
- (a) Disadvantage: PLA is more expensive / requires land to grow crops / may compete with food production / needs specific industrial composting conditions (1)
- (b) Judgment with valid reason (1) — e.g., PLA is better for the environment, OR poly(ethene) is cheaper/more durable
GCSE Perfect