2.2 - soaps, detergents and emulsifiers Flashcards
what is another word for salts of long-chain fatty acids?
soaps
what are the two stages of hydrolysing an ester?
- alkali hydrolyses the fat/oil molecule
- alkali neutralises the fatty acids to form salts (soap)
describe the structure of a soap
- the long covalent hydrocarbon chain that makes up the tail section of a soap structure is covalent (non-polar) and therefore oil-soluble, this is called hydrophobic and it is not soluble in water
- the carboxylate group that makes up the head of the molecule is ionic and therefore water-soluble, this is called hydrophilic, this is not soluble in non-polar solvents such as oil
explain the cleansing action of soap
- soap molecules have an ionic head part and a covalent tail
- ionic/polar head dissolves in water/is hydrophilic and the covalent tail dissolves in oil and is hydrophobic
- agitation separates oil from the surface/cause small oil droplets (micelles) to form
- the negatively charged ball like structures repel eachother and the oil or grease is kept suspended in the water forming an emulsion
what is hard water?
large concentration of calcium and magnesium ions dissolved
what happens when soaps are used with hard water?
- instead of forming a soapy lather, a white precipitate called scum is formed
- this is because the calcium and magnesium ions react with the soap molecules to form insoluble substances
- the precipitates reduce the cleansing action of the soap
what is best to use in areas with hard water?
soapless detergents as these do not form a scum
describe the structure of detergents
detergents have a soap-like structure with a long hydrocarbon tail, but instead of the ionic carboxylate group at the end of the molecule there is a sulfonate group ‘SO3’
what is the term used to describe oil and water regarding emulsions?
immiscible (this means they do not mix)
what is an emulsifier?
- a substance which prevents the separation of polar and non-polar substances
- a molecule that contains a hydrophilic part and a hydrophobic part to their structures
what is an emulsion?
droplets of one liquid suspended in another
what happens when an emulsifier is added to oil and water?
once an emulsifier, such as soap is added, the oil is able to disperse throughout the water (emulsion)
how are emulsifiers formed in the food industry?
- by reacting an edible oil with glycerol
- the emulsifier produced could have OH groups or an ionic part which is hydrophilic as well as a long-chained hydrocarbon part which is hydrophobic
what is the ratio in which fats and oils combine?
one glycerol molecule to three molecules of fatty acid
