Ethanol and ethanoic acid

Ethanol (alcohol) is a liquid that mixes well with water. It is a good solvent, used in medicines such as tincture iodine and cough syrups.

A clear warning from the book. Drinking even small amounts of pure ethanol (absolute alcohol) can kill, and drinking alcohol over a long time causes many health problems. Methanol is even more dangerous: very small amounts can cause blindness and death. Alcohol made for industry is mixed with methanol and coloured blue so no one drinks it: this is denatured alcohol.

Ethanol reacts with sodium and gives off hydrogen:

2Na + 2CH₃CH₂OH → 2CH₃CH₂ONa + H₂

Heated with hot concentrated sulphuric acid, it loses water and becomes ethene.

A good use: sugarcane turns sunlight into chemical energy very well. Its juice gives molasses, which is fermented into ethanol. Ethanol is mixed into petrol because it is a cleaner fuel: it burns to give only carbon dioxide and water.

Ethanoic acid is acetic acid. A 5–8% solution of it in water is vinegar. Pure ethanoic acid freezes at 290 K, which is 17 °C, so on a cold day it freezes into ice-like crystals. That is why it is called glacial acetic acid. It is a weak acid.

Esterification: ethanoic acid + ethanol, with a little acid as catalyst, gives a sweet-smelling ester, used in perfumes and flavours. Heat an ester with sodium hydroxide and it splits back into an alcohol and a sodium salt. This is saponification, and it is how soap is made.

Telling the two apart: ethanoic acid reacts with sodium carbonate or sodium hydrogencarbonate and fizzes, giving carbon dioxide that turns lime water milky. Ethanol does not. Ethanoic acid also reacts with bases: NaOH + CH₃COOH → CH₃COONa + H₂O.