Organic Chemistry: notes

Crude Oil and Hydrocarbons

• Fractional distillation: crude oil is heated and split into fractions by boiling point. Small molecules with low boiling points rise to the top of the column.
• Alkanes: hydrocarbons with single bonds only, general formula CnH2n+2. Methane, CH4, is the main gas in natural gas.
• Alkenes: hydrocarbons with a double bond, general formula CnH2n. Ethene, C2H4, is used to make plastics.
• Cracking: long alkanes are broken into shorter, more useful molecules using heat and a catalyst. Decane (C10H22) gives octane (C8H18) and ethene (C2H4).

Reactions

• Addition reaction: atoms add across the double bond, which becomes single. Ethene + hydrogen gives ethane, using a nickel catalyst.
• Bromine test: alkenes turn bromine water from orange to colourless. Alkanes do not change colour.
• Ethanol: an alcohol with the OH group, made by fermenting sugar with yeast, or by reacting ethene with steam. Ethanol is C2H5OH.
• Carboxylic acids: contain the COOH group. Ethanoic acid, CH3COOH, is the acid in vinegar.
• Esters: formed when an alcohol and a carboxylic acid react, with concentrated H2SO4 as catalyst. Ethanol + ethanoic acid gives ethyl ethanoate + water. Esters smell fruity and are used in flavourings.

Polymers and Soaps

• Addition polymerisation: many small alkene molecules (monomers) join to form a long chain polymer. Ethene gives poly(ethene), used for plastic bags.
• Natural macromolecules: proteins, starch, cellulose and rubber are natural polymers. Starch is built from glucose units.
• Soaps: made by heating a fat or oil with sodium hydroxide. Soap molecules let grease mix with water, so dirt can be washed away.