The alkanes are a family of hydrocarbons- they contain only hydrogen and carbon.
- Methane- CH4
- Ethane- C2H6
- Propane- C3H8
- Butane- C4H10
Alkanes burn in air and the combustion products are carbon dioxide and water.
Alkanes are good fuels.
Alkanes do not react with solutions of acid or alkalis because the C-C and C-H bonds in alkane molecules are unreactive.
Alcohols contain an -OH functional group.
- Methanol- CH3OH
- Ethanol- C2H5OH
- Propanol- C3H7OH
- Butanol- C5H9OH
Ethanol is used in many different ways
- As a solvent e.g in perfumes
- As a fuel
- In drinks like beer, wine and vodka
The chemical industry used methanol as a raw material to make glues, foams and windscreen washer fluid.
Physical Properties Of Alcohols
Alcohols with long hydrocarbon chains do not mix with water (like heptanol C7H15OH) because the hydrocarbon chain does not interact with water molecules.
Ethanol boils at 79 degrees celsius. Propane, with a similar relative formula mass to ethanol, boils at -42 degrees celsius.
The alcohol has a higher boiling point because -OH groups tend to pull its molecules together.
Ethanol has a lower boiling point than water because there are only weak attractive forces between the hydrocarbon parts of the molecule. So ethanol molecules are held together less strongly than water molecules.
Chemical Properties Of Alcohols
Alcohols contain a hydrocarbon chain, so they burn in air. The products are carbon dioxide and water.
Alcohols react with sodium. When ethanol reacts with soduim, the products are soduim ethoxide and hydrogen.
Water reacts with sodium in the same way; the products are sodium hydroxide and hydrogen.
The reactions are similar because both water and ethanol contain an -OH group. When they react an O-H bond breaks.
Sodium ethoxide and sodium hydroxide are both salts.
Alkanes do not react with sodium. This is because alkanes have no -OH group. Their C-C and C-H bonds are unreactive.
Carboxylic acids contain this functional group
- Methanoic acid- HCOOH
- Ethanoic acid- CH3COOH
Vinegar is a dilute solution of ethanoic acid in water.
Some carboxylic acids smell and taste bad, like the ones in sweaty socks and rancid butter.
Carboxylic acids are weak acids- only a few molecules are ionized at any one time.
Carboxylic acids react with metals, alkalis and carbonates.
Esters contain this functional group
Esters are responsible for the smells and flavours of fruits. We use esters:
- To flavour foods
- To make sweet smelling perfumes, shampoos and bubble baths
- As solvents
- As plasicisers to make polymers like PVC soft and flexible
You can make an ester by warming a mixture of an alcohol and a carboxylic acid.
You also need a small amount of sulfuric acid as a catalyst.
Ethanoic acid + Methanol --> methyl ethanoate + water
This equation summarises the reaction for making ester methyl ethanoate.
How to make an ester- methyl ethanoate.
1) Heat the ethanol, ethanoic acid with concentrated sulfuric acid.
2) Heat the reaction mixture after refluxing
3) Shake the impure product with reagents in aqueous solution to remove impurities
Fats and oils
Plants and animals make fats and oils as energy stores. Fats and oils are esters of
- Gycerol, an alcohol with 3 -OH groups
- fatty acids, which have a long hydrocarbon chain attatched to a -COOH group
Animal fats like butter and lard are usually solid at room temperature. All bonds between carbon atoms are single bonds (C-C) . The molecules are saturated- no more hydrogen atoms can be added to them.
Vegetable oils, like sunflower oil are usually liquid at room temperature. There are double bonds between some carbon atoms (C=C). The molecules are unsaturated- more hydrogen atoms can be added to them.