Addition, condensation & natural polymers (Chem only) – GCSE Chemistry exam questions with mark scheme

1Grade 6–7Triple only3 marks

The diagram shows a molecule of chloroethene.

(a) Chloroethene forms an addition polymer. Draw the repeating unit of the polymer. [2]

(b) Explain why chloroethene can form an addition polymer but chloroethane cannot. [1]

(a) two carbons joined by a single C–C bond, with H, H, H and Cl attached correctly; allow Cl on either carbon(1)
(a) brackets drawn through extended bonds on each side, with n after the bracket(1)
(b) chloroethene has a C=C (double) bond / is unsaturated; chloroethane does not(1)
Answer: (a) –[CH₂–CHCl]–_n drawn displayed with bonds through brackets (b) chloroethene has a C=C double bond
Examiner tip: The bonds must go through the brackets, and the double bond becomes single in the repeating unit.

2Grade 6–7HigherTriple only4 marks

Polyesters are made by condensation polymerisation.

(a) A polyester is made from a monomer with two –OH groups and a monomer with two –COOH groups. Give the name of the small molecule also produced. [1]

(b) Give two differences between addition and condensation polymerisation. [2]

(a) water; allow H₂O(1)
(b) any two from (each must compare both types): addition gives only one product (the polymer) whereas condensation also gives a small molecule (e.g. water); addition monomers have a C=C double bond whereas condensation monomers have two functional groups (each); addition usually uses one type of monomer whereas condensation usually uses two (different) monomers — first difference(1)
(b) second correct difference from the list above; a statement about only one type of polymerisation does not score(1)
(c) amino acids; allow amino acid(1)
Answer: (a) water (b) any two of: condensation also forms a small molecule (addition forms only the polymer); condensation monomers have two functional groups (addition monomers have C=C); condensation usually uses two monomers (addition usually one) (c) amino acids
Examiner tip: A 'difference' must compare both types — say what each one does.

3Grade 1–3FoundationTriple only4 marks

The table shows the formulae of four compounds.

Compound	Formula
A	CH₄
B	C₂H₆
C	C₃H₆
D	C₂H₅OH

(a) Which compound, A, B, C or D, can be used to make an addition polymer? [1]

(b) Give the reason for your answer to part (a). [1]

(d) The formula of a polymer is often written with a letter n after the brackets. What does n represent? [1]

(a) C(1)
(b) it has a C=C (double) bond / it is an alkene / it is unsaturated; allow 'has a double bond'; do not accept 'it is a hydrocarbon'(1)
(c) poly(propene); allow polypropene / polypropylene; do not accept polyethene(1)
(d) a large number (of repeating units / of monomers joined); accept 'many' or 'thousands'; do not accept 'number of atoms'(1)
Answer: (a) C (b) it has a C=C double bond (is an alkene) (c) poly(propene) (d) a large number of repeating units
Examiner tip: In (b), 'it is a hydrocarbon' scores nothing: B is also a hydrocarbon. You must name the C=C double bond.

4Grade 4–5Triple only3 marks

The diagram shows the repeating unit of an addition polymer. CN is a group of atoms that stays unchanged during polymerisation.

(a) Draw the displayed formula of the monomer used to make this polymer. Show the CN group as CN. [2]

(b) The repeating unit contains exactly the same atoms as the monomer. Explain why. [1]

(a) two carbon atoms joined by a C=C double bond(1)
(a) three H atoms and one CN group correctly attached (two H on one carbon; one H and the CN on the other); no brackets or n, and no bonds extending beyond the molecule; allow CN on either carbon(1)
(b) addition polymerisation forms only one product (the polymer) / no other molecule (such as water) is lost; ignore 'atoms are conserved' alone(1)
Answer: (a) CH₂=CHCN drawn displayed: H₂C=CH–CN with C=C double bond (b) only one product is formed in addition polymerisation, so no atoms are lost
Examiner tip: Drop the brackets, the n and the two extension bonds, and turn the C–C into C=C; leaving trailing bonds loses the second mark.

5Grade 6–7Triple only4 marks

A sample of poly(propene) is made from propene, C₃H₆.

One molecule of the poly(propene) has a relative formula mass (M_r) of 126 000.

Relative atomic masses (A_r): C = 12, H = 1

(a) Calculate the number of propene molecules that joined together to make one molecule of this poly(propene). [3]

(b) A factory converts 2.1 tonnes of propene completely into poly(propene). What mass of poly(propene) is produced? Give a reason for your answer. [1]

(a) M_r of propene = (3 × 12) + (6 × 1) = 42(1)
(a) M_r of repeating unit is the same as the monomer / 126 000 ÷ 42(1)
(a) = 3000; correct answer with no working scores 3 marks(1)
(b) 2.1 tonnes and addition polymerisation has only one product / no atoms are lost; both needed for the mark(1)
Answer: (a) 3000 (b) 2.1 tonnes, because the polymer is the only product
Examiner tip: Students who subtract water from the monomer here are mixing up addition and condensation: in an addition polymer the repeating unit has the same M_r as the monomer.

6Grade 8–9HigherTriple only5 marks

A polyester can be made from the two monomers shown as block diagrams.

(a) Draw the repeating unit of the polyester formed from monomers A and B. Use the block diagrams in your answer. [2]

(b) Monomer B is hexanedioic acid, C₆H₁₀O₄. Assume that two molecules of water are formed for every molecule of hexanedioic acid that reacts.

Calculate the maximum mass of water formed when 438 g of hexanedioic acid reacts completely with excess monomer A.

Relative atomic masses (A_r): H = 1, C = 12, O = 16 [3]

(a) one open block and one filled block joined by an ester link, e.g. –O–□–O–C(=O)–■–C(=O)–; allow –OOC–■–COO–□– ; allow ester link drawn displayed(1)
(a) only one of each block, with one bond extending at each end through brackets (allow n not shown); no OH or H left on the ends(1)
(b) M_r(C₆H₁₀O₄) = 146 and moles = 438 ÷ 146 = 3.00 (mol)(1)
(b) moles of water = 2 × 3.00 = 6.00 (mol)(1)
(b) mass of water = 6.00 × 18 = 108 (g); allow ecf from incorrect moles; correct answer with no working scores 3 marks(1)
Answer: (a) –[O–□–O–CO–■–CO]–_n (b) 108 g
Examiner tip: In the repeating unit the –OH from the acid and the H from the alcohol have gone (as water), so do not leave OH or H on the ends of the brackets.

7Grade 6–7HigherTriple only4 marks

Glycine (H₂NCH₂COOH) and alanine (H₂NCH(CH₃)COOH) are amino acids.

(a) Name the two functional groups present in every amino acid. [1]

(b) One molecule of glycine reacts with one molecule of alanine to form a dipeptide. Name the other product of this reaction. [1]

(d) A polypeptide chain is made from 120 amino acid molecules joined in a single chain. How many water molecules are released when this chain forms? [1]

(a) amine / amino (–NH₂) and carboxylic acid (–COOH); allow carboxyl; both needed; formulae alone acceptable(1)
(b) water / H₂O(1)
(c) 75 + 89 − 18 = 146(1)
(d) 119(1)
Answer: (a) amine (–NH₂) and carboxylic acid (–COOH) (b) water (c) 146 (d) 119
Examiner tip: One water molecule is lost for each new link, not for each amino acid: a chain of 120 has 119 links.

8Grade 4–5Triple only5 marks

DNA, starch and cellulose are naturally occurring polymers.

(a) Name the type of monomer that makes up:

(i) cellulose [1]

(ii) DNA. [1]

(b) Describe the structure of a DNA molecule. [2]

(a)(i) sugars; allow glucose; ignore carbohydrate(1)
(a)(ii) nucleotides; do not accept nucleic acids or bases(1)
(b) two polymer chains / strands(1)
(b) in the form of a double helix or made from four different (nucleotide) monomers(1)
(c) (encodes) genetic instructions (for the development and functioning of living organisms and viruses); allow carries genetic information / genetic code(1)
Answer: (a)(i) sugars (ii) nucleotides (b) two polymer chains, made from four different nucleotides, in a double helix (c) encodes the genetic instructions for living organisms
Examiner tip: Students often write 'amino acids' or 'bases' for DNA: the monomers are nucleotides.

9Grade 6–7HigherTriple only4 marks

A company makes two polymers, X and Y. The table shows data for one batch of each.

Polymer	Number of different monomers	Total mass of monomers used in kg	Mass of polymer formed in kg
X	1	560	560
Y	2	520	430

All of the monomers react in each batch.

(a) Which polymer, X or Y, is made by condensation polymerisation? Give a reason based on the masses in the table. [2]

(b) Calculate the mass of the other product formed in the batch of polymer Y. [1]

(a) Y(1)
(a) mass of polymer is less than the mass of monomers (by 90 kg) so a small molecule / another product (such as water) is also formed; reason must use the mass data; ignore ‘Y is made from two (different) monomers’ alone(1)
(b) 520 − 430 = 90 (kg)(1)
(c) so that each monomer can react / form a bond at both ends, allowing the chain to keep growing / to form a long chain; ignore 'to make a polymer' alone(1)
Answer: (a) Y; the polymer mass (430 kg) is less than the monomer mass (520 kg), so a small molecule such as water is also made (b) 90 kg (c) each monomer can link at both ends so a long chain forms
Examiner tip: For the reason in (a) you must quote the data: 'Y has two monomers' alone does not show a small molecule is lost.

10Grade 8–9HigherTriple only6 marks

Poly(propene) is made from propene, CH₂=CHCH₃.

A polypeptide can be made from amino acids such as glycine, H₂NCH₂COOH.

Compare how poly(propene) and a polypeptide are formed from their monomers. [6]

poly(propene) is made by addition polymerisation; a polypeptide by condensation polymerisation(1)
propene has a C=C double bond / is unsaturated(1)
the C=C bond opens / breaks so the carbon atoms of many monomers join by single C–C bonds(1)
amino acids have two different functional groups: amine (–NH₂) and carboxylic acid (–COOH)(1)
the –NH₂ of one amino acid reacts with the –COOH of another(1)
addition: the polymer is the only product; condensation: water (a small molecule) is also released at each link(1)
addition: the repeating unit has the same atoms as the monomer; condensation: the repeating unit has fewer atoms than the monomers (H₂O lost)(1)
poly(propene) uses one type of monomer; a polypeptide / protein can be made from different amino acids(1)
similarity: both join many small monomer molecules into long chains(1)

Level	Marks	What it looks like
Level 3	5–6	Clear, detailed comparison of both processes, linking the functional groups in each monomer to how the bonds form and to the products; at least one explicit similarity or difference is drawn between the two.
Level 2	3–4	Correct description of both processes with some links to functional groups or products, but the comparison is mostly implied or some detail is missing.
Level 1	1–2	Simple, mostly separate statements about one or both processes, e.g. naming addition and condensation, with little or no explanation.
No relevant content	0	No relevant content.

Answer: Indicative: addition vs condensation; C=C opens vs –NH₂ reacting with –COOH; one product vs water also formed; repeat unit same atoms as monomer vs loses H₂O; both form long chains of many monomers.
Examiner tip: 'Compare' needs both sides of each point: say what happens in poly(propene) and what happens in the polypeptide, not two separate descriptions.

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