How to deduce the polymerisation reaction for any alkene
3 marks · NormalA sample of poly(ethene) contains 250 repeat units. Each repeat unit has the formula -CH2CH2-.
Calculate the total number of carbon atoms and hydrogen atoms in the polymer chain.
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Show answer
500 carbon atoms, 1000 hydrogen atoms
Also accept: Working that multiplies the number of repeat units by atom count per unit
Common mistakes: Dividing atoms instead of multiplying; Incorrect addition of atoms
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Identifies or states atoms in one repeat unit: 2 C and 4 H.
M2 · 1 mark · Multiplies the number of atoms in one repeat unit by 250 to find total atoms. (follow-through)
A1 · 1 mark · Gives final answers: 500 C atoms, 1000 H atoms. (follow-through)
Worked solution
Each repeat unit has 2 C and 4 H atoms (-CH2CH2-).
Number of C atoms: 2 × 250 = 500.
Number of H atoms: 4 × 250 = 1000.
Final answers: 500 carbon atoms and 1000 hydrogen atoms.