OCR A-Level Chemistry AS Breadth in chemistry (01), June 2019: Question 17

1 mark · Medium difficulty · Multiple Choice

Identify the monomer that forms the given addition polymer section containing repeating CN groups.

Practise this question

Question

Multiple-choice question 17 showing a section of an addition polymer with a carbon backbone and pendant CN groups attached to every other carbon. Four options are given: A, CH3CH(OH)CN; B, HOCH2CH2CN; C, H2C=CHCN; D, NCCH=CHCN. A blank answer box is provided at the bottom with a mark allocation of [1].
Question text

17 A section of a polymer is shown below.

CN CN CN

Which monomer could form this polymer?

A CH3CH(OH)CN

B HOCH2CH2CN

C H2C=CHCN

D NCCH=CHCN

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme for question 17 showing the correct answer is C.

17 C 1 AO1.2

How to answer it

Identifying Monomers from Addition Polymers

What this question tests

This question assesses your understanding of addition polymerisation (AO1.2). Specifically, it tests your ability to look at a repeating section of a carbon-chain polymer skeleton, locate the repeating unit, break the carbon-carbon single bond back down into a double bond, and match it to the correct alkene monomer.

Question 17 Analysis

Identifying the Monomer from a Polymer Chain

✅ Correct Answer

C ( H₂C=CHCN )

The polymer shown is poly(acrylonitrile), formed by the addition polymerisation of propeninitrile ( H₂C=CHCN ).

💡 Key Knowledge

  • Addition polymers form from alkenes through addition polymerisation (no small molecules eliminated).
  • The repeating unit of an addition polymer always features a 2-carbon backbone ( -C-C- ).
  • To find the monomer, isolate the repeating unit (2 carbons in the main chain) and convert the single bond between them into a double bond ( C=C ).

🧠 Exam Technique

  • Scan the options for functional groups: the polymer chain has a pendant -CN group on every alternate carbon, ruling out monomers with hydroxyl ( -OH ) groups like A and B.
  • Between C and D, check the carbon backbone length. The repeating unit has a 2-carbon chain, meaning the monomer must contain 2 carbons in its principal chain, pointing directly to H₂C=CHCN (C).

❌ Common Errors

Students often select options A or B because they recognise -CN and -OH chemistry, forgetting that addition polymers are formed specifically from alkenes (unsaturated monomers), not substituted alkanes or condensation molecules.

Mark Allocation: [1] mark available for choosing option C. Tested under Assessment Objective AO1.2 (Demonstrating knowledge and understanding of scientific ideas).

Topics

Module 4: Core organic chemistry · 4.1 Basic concepts and hydrocarbons

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), June 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.