Alkenes & Further Organic Chemistry

IGCSE Edexcel Chemistry
4.19–4.28 Alkenes, addition reactions, polymers, alcohols and carboxylic acids
Key Concepts: Alkenes are unsaturated hydrocarbons containing a C=C double bond. They undergo addition reactions and can form addition polymers. Alcohols contain the –OH group; carboxylic acids contain –COOH.

Section A — Alkenes

1. State the general formula for alkenes and explain why they are described as unsaturated. [3]
2. Complete the table for the first three alkenes. [6]
NameMolecular formulaStructural formula
Ethene
Propene
Butene
3. Draw the displayed formula for ethene (C₂H₄). Show the double bond clearly. [2]

Section B — Addition Reactions of Alkenes

4. Describe the test for alkenes using bromine water. State the observation and explain what it shows. [3]
5. Write the word equation and balanced symbol equation for the reaction between ethene and bromine. [3]
6. Name the product formed and the type of reaction when ethene reacts with: [4]

a) Hydrogen (H₂)

b) Water (steam, H₂O)

c) Hydrogen chloride (HCl)

d) Bromine (Br₂)

Section C — Addition Polymerisation

7. Define addition polymerisation. [2]
8. Draw the repeat unit of poly(ethene). [2]
9. Name the monomer used to make each polymer. [3]
PolymerMonomer
Poly(propene)
Poly(chloroethene) / PVC
PTFE

Section D — Alcohols

10. State the functional group of alcohols and give the name and formula of the first two members of the homologous series. [4]
11. Ethanol can be produced by fermentation. Write the equation and state the conditions required. [4]
12. State the products when ethanol burns completely in air. [2]

Section E — Carboxylic Acids

13. State the functional group of carboxylic acids. Name the simplest carboxylic acid and write its formula. [3]
14. Ethanol can be oxidised to ethanoic acid. Describe how this happens in the production of vinegar. [2]

Total marks: 43

Mark Scheme

1. CnH2n [1]; unsaturated means the molecule contains a carbon-carbon double bond (C=C) [1]; it can undergo addition reactions to add atoms across the double bond [1] [3]
2. Ethene: C₂H₄, CH₂=CH₂; Propene: C₃H₆, CH₃CH=CH₂; Butene: C₄H₈, CH₃CH₂CH=CH₂ [6 — 2 per row]
3. H₂C=CH₂ with two lines between carbons for double bond; correct bonds to H [2]
4. Add bromine water to the sample [1]; orange/brown colour decolourises to colourless [1]; shows the compound is unsaturated (contains a C=C double bond) [1] [3]
5. Ethene + bromine → 1,2-dibromoethane [1]; C₂H₄ + Br₂ → C₂H₄Br₂ [2] [3]
6. a) Ethane; addition (hydrogenation); b) Ethanol; addition (hydration); c) Chloroethane; addition; d) 1,2-dibromoethane; addition [4]
7. Many small monomer molecules containing C=C double bonds [1]; join together by opening the double bonds to form a long polymer chain [1] [2]
8. –[CH₂–CH₂]n– (bracket notation with CH₂–CH₂ as repeat unit) [2]
9. Poly(propene): propene; PVC: chloroethene (vinyl chloride); PTFE: tetrafluoroethene [3]
10. Functional group: –OH (hydroxyl) [1]; methanol CH₃OH [1]; ethanol C₂H₅OH [1] (1 mark for first two correct names/formulae) [4]
11. C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (glucose → ethanol + carbon dioxide) [2]; conditions: yeast [1]; warm temperature ~30–40°C / no oxygen (anaerobic) [1] [4]
12. Carbon dioxide and water [2]
13. Functional group: –COOH (carboxyl group) [1]; simplest: methanoic acid, HCOOH [2] [3]
14. Ethanol is oxidised by bacteria (or air/oxygen) [1]; bacteria convert ethanol to ethanoic acid (the acid component of vinegar), CH₃COOH [1] [2]