Combustion: alkanes and alcohols burn completely in plenty of oxygen to make carbon dioxide and water. For methane, CH4 + 2O2 → CO2 + 2H2O. For ethanol, C2H5OH + 3O2 → 2CO2 + 3H2O.
Alkenes take part in addition reactions. The C=C double bond opens and each carbon atom gains an atom, so only one product is made. With bromine, ethene makes 1,2-dibromoethane, C2H4Br2, and orange bromine water turns colourless. This is the test for a double bond. With hydrogen and a nickel catalyst, ethene makes ethane, an alkane with only single bonds.
Alcohols are oxidised to carboxylic acids when heated with acidified potassium manganate(VII), which turns from purple to colourless. Ethanol makes ethanoic acid, methanol makes methanoic acid and propanol makes propanoic acid. The same pattern works for each alcohol.
