Chemistry 9701 · AS & A Level · Polymerisation

Polymerisation — practice question

Growing concern about the shrinking availability of crude oil has led to many efforts to replace oil-derived polymers with polymers made from natural sources. One example is ‘polylactide’ or PLA, which is made from corn starch and is used in a variety of ways.
(a)[2]

(i) Calcium hydroxide is added to the fermentation tanks so that lactic acid production does not slow down. Why could a high acidity level make the enzymes less effective? (ii) The structure of lactic acid is shown. What kind of reaction occurs in this polymerisation?

(b)[1]

Lactic acid occurs in two stereoisomeric forms. Draw the other form inside the box.

(a(i))

Calcium hydroxide is added to the fermentation tanks so that lactic acid production does not slow down. Why could a high acidity level make the enzymes less effective?

(a(ii))[2]

The structure of lactic acid is shown. What kind of reaction occurs in this polymerisation?

(c(i))

Explain why PLA would not be a suitable packaging material for foods preserved in vinegar.

(c(ii))[2]

PLA containers are not used for hot drinks. Suggest why.

(d(i))

Draw a section of the co-polymer showing one repeat unit.

(d(ii))

Suggest what type(s) of bonding will occur between chains of this co-polymer, indicating the groups involved.

(d(iii))

Suggest one property in which the co-polymer differs from PLA.

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