GCSE & A Level Revision Notes
Subject: Chemistry
Level: IGCSE
Exam Boards: EDEXCEL
Section 3 (3.1-3.12)
Organic Chemistry
3.1
Homologous series: A family of compounds that have similar properties and bonding, such as the alkenes or alcohols
Hydrocarbon: A compound containing hydrogen and carbon only
Saturated: Contains only single bonds
Unsaturated: Contains a double bond
General Formula: e.g. CnH2n A formula that fits all the members in a homologous series
Isomerism: Where molecules have the same molecular formula but a different structural or displayed formula.
Alkanes
3.2
Alkanes have the general formula of CnH2n+2
3.3
 |
 |
 |
 |
|---|---|---|---|
| Methane (CH4) | Ethane (C2H6) | Propane (C3H8) | Butane (C4H10) |
3.4
Different products come from combustion of hydrocarbons.
- Complete combustion – Carbon Dioxide
- Incomplete combustion – Carbon Monoxide
- Very Incomplete combustion – carbon (soot)
3.5*
CH4 + Br2 → CH3Br + HBr Under UV light, bromine substitutes with hydrogen into methane to produce bromomethane.
Alkenes
3.6
Alkenes are another homologous series. They have a general formula of CnH2n.
3.7
 |
 |
| Methane (CH4) | Ethane (C2H6) |
3.8
A test for alkenes is an addition reaction with bromine water. The bromine water, which starts brown, goes colourless. C2H4 + Br2 → C2H4Br2
3.9
Ethanol can be manufactured by passing ethene and steam over phosphoric acid, which acts as a catalyst, at a temperature of around 300˚C and a pressure of around 60-70 atmospheres.
3.10
Ethanol can also be manufactured by the fermentation of sugar by yeast, which takes place at a temperature of around 30˚C. C6H12O6 → 2C2H5OH + 2CO2
| Fermentation | Hydration of Ethene | |
|---|---|---|
| Raw Materials | Renewable resources | Non-renewable (crude oil) |
| Process | Batch | Continuous |
| Rate of reaction | Very slow | Fast |
| Quality | Dilute solution- needs processing | Pure ethanol |
| Conditions | Low temperature + pressure | Very high temperature and pressure – incurs costs |
3.11
Ethanol can be dehydrated, by passing it over hot AlO3. This acts as a catalyst to speed up the reaction.
C2H5OH → C2H4 + H2O
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