soaps, setergents and emulsions 1 Flashcards
Describe the formation of soaps
Fats and oils are esters. when theyr are hydrolysed using alkali, salts of the long chain fatty acids are formed.
Glycerol is also formed
Describe the structure of soap molecules
A soap molecule has a long covalent hydrocarbon part, often referred to as the tail ad an ionic part, often referred to as the head.
Describe the properties of ‘the tail’ in soaps
covalent and non-polar therefore insoluble in water.
Termed hydrophobic ‘water-hating’
It is however soluble in covalent substances
Describe the properties of ‘the head’ of the soap ion
negatively charged
termed hydrophilic ‘water-loving’
it is polar so it’s soluble in water
Describe the cleansing action of soap
When soap is used to clean oil and grease. Agitation causes small grease droplets (micelles) to form in the water. The negative charge on the heads repel each other and prevent the globules of oil from recombining. This allows the oil and grease to be washed off the surface.
What is one problem with soap
that it does not lather well in hard-water areas.
what is a hard-water
Hard water contains calcium and magnesium ions. Insoluble salts like calcium stearate, known as scum, form. Detergents have been developed that do not form scum
What are detergents
detergents are cleaning agents which work in a similar way to soaps, but have the advantage of not forming insoluble salts in hard water, this means they can form a lather.
examples of detergents
alkylbenezesulfonates
example: dodecylbenzenesulfonate
Why are detergents similar to soaps
They have a similar structure. hydrocarbon hydrophobic tail and ionic (negative) hydriphillic head. As a result they clean in the same way as soaps
Most common way of making dodecylbenzensulfonate
by reacting benzene with dodecene and sulfur trioxide to give the sulfonic acid. The sulfonic acid is then neutralised with sodium hydroxide.
describe emulsions
what do emulsifiers allow
normally immiscible liquids to mix and stop them from separating
What are emulsions in food
mixture of fat/oil and water
What are emulsifiers
are soap like molecules that can be made by reacting edible oils with glycerol.
How many fatty acids and where are they in emulsifiers
one or 2 fatty acid groups are attached to the glycerol backbone
rather than the three in fats/oils
describe the hydrophobic and hydrophilic in emulsifiers
emulsifier has molecules with a hydrophobic part (the fatty acid ‘tail’) and a hydrophilic part - one or two hydroxyl groups or other water-soluble parts
