C3.6 Alcohols, carboxylic acids and esters

Organic molecules that form the basis of all living things all contain carbon atoms. The study of these molecules is known as organic chemistry.

A functional group is a group of atoms that give organic compounds their characteristic reactions. The functional group of an alcohol is OH. A homologous series is a family of compounds with the same functional group. The first 3 members of the homologous series of alcohol are methanol, ethanol and propanol. These will dissolve in water to form a neutral solution.

The general formula for an alcohol is CnH2n+1OH. OH must be shown to declare the functional group. This is why ethanol is not written as C2H6O.

Alcohols can be used as solvents, fuels in alcoholic drinks and in perfumes. Octanol is used in perfumes as it evaporates slowly, this means perfume stays on skin for a longer period of time. Drinking too much ethanol in alcohol can lead to high blood pressue and heart disease.

The chemical formula for ethanol is C2H5OH, it can be produced by the fermentation of plants;

sugar=yeast=>CO2 + C2H5OH.

Ethanol can also be produced by hydrating ethene with steam;

C2H4+H2O => C2H5OH

Ethanol can be oxidised to form ethanoic acid by boiling with potassium dichromate solution or by exposing to air. Although ethanol is renewable and carbon neutral the land used could be used for crops and habitats are destroyed.

Combustion;

Ethanol + oxygen => carbon dioxide + water

Ethanoic acid is a member of the carboxylic acids which have a functional group -COOH. Carboxylic acids form acidic solutions when dissolved in water and still have the typical reactions of acids. Solutions of carboxylic acids have a pH value less than 7. Carbonates gently fizz in their acidic solutions releasing carbon dioxide.

Strong acids ionise completely in a solution, molecules in weak acids stay as they are. Only some will ionise (split up) in their solutions. Therefore the strong acid will have a higher concentration of H+ ions than the weak acid

Aqueous solutions of weak acids have a higher pH value than solutions of strong acids with the same concentration. Esters are made by reacting a carboxylic acid and an alcohol together with an acid catalyst, usually sulfuric acid. Esters are volatile compounds used in flavourings and perfumes.

Alcohols, carboxylic acids and esters have many uses which benefit society. However the use of substances such as ethanol and solvents can be abused. Alcohol has been associated with high blood pressure and heart disease. Excess alcohol can also damage the liver.

Ethanol is used in methylated spirits as a solvent, some alcoholics will drink this due to the contence. Drinking 'meths' causes liver failure, blindness and an early death so other chemicals are added to spirits to make it more difficult to distil the ethanol.

In the future biofuels such as ethanol and esters could help society because crude oil supplies are running out. However this need of supply may conflict with the need to feed the world.