Q73 · Practice questionSimple familiar3 marks
QUESTION 73 (3 marks)
Poly(lactic acid), PLA, has ester links in its backbone. Polyethene has a carbon–carbon backbone.
a) Explain why PLA can undergo hydrolysis but polyethene does not undergo the same reaction. [2 marks]
b) Predict how this structural difference can affect biodegradability. [1 marks]
WORKED SOLUTION
3 marksPractice marking scheme
PLA has hydrolysable ester bonds that can split into shorter chains; polyethene lacks these functional groups. PLA is therefore generally more susceptible to biodegradation under suitable conditions.
Water, aided by catalysts or enzymes, can cleave PLA ester links. C–C backbone bonds do not hydrolyse like esters. Shorter products are more accessible to biological breakdown; actual degradation still depends on conditions.
- Identifies ester links as hydrolysable. [1 marks]
- Contrasts the C–C backbone of polyethene. [1 marks]
- Links chain cleavage to increased biodegradation under suitable conditions. [1 marks]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
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