O-Level and SEC G3 Chemistry K324
C11: Organic Chemistry
Recognise homologous series, structures, reactions, polymers, and property trends within the current syllabus scope.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Organic Chemistry follows carbon compounds from fuel sources and refinery fractions through hydrocarbons, alcohols, carboxylic acids, esters, and polymers. K324 also includes food-oil hydrogenation, polyester hydrolysis, and recycling trade-offs, so the chapter must extend beyond naming simple alkanes and alkenes.
Resources, fractions and hydrocarbons
Natural gas, mainly methane, and crude oil are non-renewable. Crude oil is a hydrocarbon mixture separated by fractional distillation because components have different boiling ranges. Fractions compete as fuels and chemical feedstocks. Bioethanol from sugarcane is renewable, but sustainability comparisons must consider carbon dioxide, land, processing, and the evidence supplied.
Alkanes are saturated hydrocarbons with general formula CnH2n+2; alkenes are unsaturated with CnH2n. Learn structures and names in the stated C1 to C4 range, recognise structural isomers, and use aqueous bromine to distinguish unsaturation. Cracking forms smaller alkanes, alkenes, and hydrogen to better match demand.
Reactions and functional groups
Alkanes undergo combustion and chlorine substitution. Alkenes undergo combustion, addition of bromine, steam, or hydrogen, and addition polymerisation. Polyunsaturated oils contain more than one carbon-carbon double bond per molecule; hydrogen addition reduces unsaturation and helps convert vegetable oil into a more solid margarine product.
Alcohols contain and can combust or oxidise to carboxylic acids. Ethanol forms by fermentation of glucose or catalytic hydration of ethene. Carboxylic acids contain , are weak acids, and react with carbonates, bases, and some metals. An alcohol and carboxylic acid form an ester; derive an ester name from the alcohol-derived alkyl part and acid-derived carboxylate part.
Polymers, fibres and recycling
Polymers are large molecules built from monomers. Poly(ethene) forms by addition polymerisation. Nylon is a polyamide and Terylene is a polyester; K324 requires recognition and uses but not detailed manufacturing mechanisms. Deduce an addition-polymer repeat unit from its alkene monomer and reverse the process when asked.
Non-biodegradable plastics persist and create disposal problems. Physical recycling can melt sorted poly(ethene) into pellets. Chemical recycling can depolymerise or crack waste into monomers, feedstock, or fuel. Acid-catalysed hydrolysis can break a polyester. Discuss recycling through social, economic, and environmental trade-offs rather than claiming one method is always best.
Formulae and relationships
| Relationship | Use |
|---|---|
| General formula for an acyclic alkane. | |
| General formula for an acyclic alkene with one double bond. | |
| Represent esterification. |
Worked examples
Example 1: Ethene decolourises aqueous bromine. State what this shows and name the reaction type.
- Aqueous bromine tests for a carbon-carbon double bond.
- Decolourisation shows the hydrocarbon is unsaturated.
- Bromine adds across the double bond, so the reaction is addition.
Answer: Ethene is unsaturated and undergoes an addition reaction.
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Recognise homologous series from functional groups and general structural patterns.
- Connect names, displayed or structural formulae, reactions, and property trends.
- Distinguish addition, substitution, combustion, fermentation, oxidation, polymerisation, and hydrolysis within scope.
Official outcome coverage
K324 C11: 4 mapped outcomes, references C11(a), C11(b), C11(c), C11(d). Check the official K324 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Use bromine or combustion observations only with stated conditions and safety, and do not infer a unique organic compound from one test.
Exam traps and retrieval check
Avoid these traps
- Calling every hydrocarbon from crude oil an alkane without using structure or formula.
- Confusing cracking with fractional distillation.
- Stopping polymer coverage at poly(ethene) and omitting condensation polymers or recycling scope.
Check from memory
What does saturated mean?
The hydrocarbon has only carbon-carbon single bonds.
What two reactants form an ester?
A carboxylic acid and an alcohol.
How can a polyester be depolymerised in K324?
By acid-catalysed hydrolysis.
Pure versus Combined scope
Combined Chemistry uses the same top-level topic label but a narrower outcome set. Use the Combined component checklist before removing or adding detail.
Shared explanation source
Eclat has a related explanation in its existing IP library. It can help with the shared concept, but its IP extensions and school-sensitive scope are not automatically part of K324. Open the related IP explanation.