How to deduce the polymerisation reaction for any alkene
5 marks · HardA polymer contains the following repeat unit:
Draw the displayed formula of the monomer used to make this polymer.
Write the name and molecular formula of this monomer.
Explain why the double bond in the monomer is important for the polymerisation reaction.
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) — · must show C=C double bond between two carbons, One Br atom on one of the carbons, Each carbon has appropriate number of H atoms (CH2=CHBr)
(b) bromoethene; CH2=CHBr
(c) The double bond allows the molecules to join together; it opens up so monomers can link to form the polymer chain.
Common mistakes: Forgetting to include the double bond in the monomer; Incorrect placement of Br atom; Confusing repeat unit with monomer
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Displayed formula for bromoethene with correct structure (C=C, Br attached to one C, correct number of hydrogens).
B2 (a) · 1 mark · All bonds and atoms correctly shown (clear double bond, correct valency).
B3 (b) · 1 mark · Correct name: bromoethene.
B4 (b) · 1 mark · Correct molecular formula: CH2=CHBr.
B5 (c) · 1 mark · States that the double bond opens to allow molecules to join/polymerise.
Worked solution
a) The monomer is CH2=CHBr. The displayed formula is:
b) Name: bromoethene; Molecular formula: CH2=CHBr
c) The double bond breaks and allows each monomer molecule to connect, forming the long polymer chain.