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. C_nH_2n 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 C_nH_2n+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 C_nH_2n.

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

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