Addition polymerisation
3 marks · NormalA monomer with the formula (chloroethene) undergoes addition polymerisation to form poly(chloroethene).
Calculate the relative molecular mass (Mr) of one repeat unit of poly(chloroethene).
Show your working, including the atomic masses you use, and draw the displayed formula of the repeat unit.
Calculate the relative molecular mass (Mr) of one repeat unit of poly(chloroethene). Use these atomic masses: C = 12, H = 1, Cl = 35.5.
Draw the displayed formula of one repeat unit of poly(chloroethene).
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) 62.5 · must show working for C, H, Cl atoms: (2 x 12) + (3 x 1) + 35.5
(b) [—CH2–CHCl—] (with bonds shown) · must show Both carbon atoms with correct numbers of H and Cl shown, Single bonds only, Square brackets and n to indicate repeating unit
Common mistakes: Incorrectly doubling the mass for a single repeat unit.; Omitting the chlorine atom in mass calculation.; Drawing the displayed formula with a double bond.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correctly identifies and sums atomic masses: (2 x 12) + (3 x 1) + 35.5
A1 (a) · 1 mark · Correct final value: 62.5 (follow-through)
B1 (b) · 1 mark · Displayed formula of one repeat unit: [—CH2—CHCl—] with all bonds shown, in brackets and n.
Worked solution
a) First, work out the atoms in one repeat unit of poly(chloroethene): .
Atoms per repeat unit: 2 carbon (C), 3 hydrogen (H), 1 chlorine (Cl)
b) The displayed formula of the repeat unit is:
\[ \boxed{[-\mathrm{CH_2}-\mathrm{CHCl}-]_n} \]
where each carbon is joined with single bonds, two hydrogens on the first carbon, one hydrogen and one chlorine on the second carbon, square brackets to show the repeating structure, and the subscript n.