2.4 Soaps, detergents and emulsions

what is the structure of a soap?

A long non-polar covalent hydrocarbon 'tail' and a polar, ionic 'head', where the charge is.

what are emulsions?

a liquid which contains small droplets of another liquid, such as soapy greasy particles mixed in water. eg a mixture of oil and water.

Why is the polar head described as hydrophilic?

as it dissolves in polar solvents such as water

why is the non-polar tail of a soap molecule described as hydrophobic?

because it is repelled by water but is soluble in oil and grease

what are detergents?

compounds with a soap-like structure which allows them to remove greasy stains. they have a non-polar tail, which is oil soluble and a polar head which is water soluble.

give an example of a substance that can be sued to hydrolyse fats or oils

sodium hydroxide or potassium hydroxide

what does the structure of a soap allow us to understand?

the cleansing action as the non-polar 'tail' dissolves in non-polar substances such as grease while the polar 'head' will not

what is the main difference in structure between soaps and detergents?

the head of a detergent will always be soluble in water. this can be achieved by using heads which are negative ions, (such as the sulfate ion), positive ions or have an overall polar structure. the detergent head will never, however, be formed from a carboxylic ion. detergents, unlike soaps, will not form precipitates in hard-water areas.

how are soaps made

they are salts made form the alkaline hydrolysis of fats and oils.

what is the purpose of emulsifiers?

to keep water-soluble and oil-soluble compounds together. they are widely used in the food industry and can be recognised as they have a polar and non-polar part.