Unit 2 : Soaps, Detergents And Emulsifiers Flashcards
What happens when we hydrolyse an ester
We get back an alkanol and a carboxylic acid
What happens if we hydrolyse a fat or oil
We get back glycerol and 3 fatty acids
What are soaps
Soaps are sodium salts of fatty acids obtained by saponification of edible fats and oils
What type of head does soap have
Hydrophilic head (polar)
What type of tail does soap have
Hydrophobic (non polar)
What are micelles
Once we agitate grease and oils , we can break them up into globules. The soap particles can then use their tails to dissolve in the non-polar globules
The outside of these micelles is negatively charged. They will be suspended and held in place in water by the electrostatic attractions to the polar water molecules.
The negatively charged outside means that they will repel one-another and over-ride any LDF attractions that normally bring oil globules back together when mixed with water in the absence of soap
What is hard water
Water which contains a large amount of mineral ions, mostly calcium and magnesium ions
How is permanent hard water caused
Dissolved calcium and magnesium surfaces
How is temporary hard water caused
Dissolved calcium bicarbonate
How do you remove temporary hardness
By boiling water
What are the problems with hard water
- The Ca2+ and Mg2+ ions form an insoluble precipitate with the soap molecules. This is referred to as Scum
- This means the soap cannot perform its cleansing action and the scum can gather on clothes etc
What are soapless detergents
- Like soap, detergent molecules have a long chain of carbon and hydrogen atoms, but at the end of the molecule there is this group -SO3 - called sulphonate instead of the -COO - carboxylate group present in soap.
- There is the same non-polar (hydrophobic) tail and a polar (hydrophilic) head and the cleansing action is same as soaps
- Detergents will NOT form precipitates with Ca2+ and Mg2+ ions. This means that they can perform the cleansing action even in hard water.
What are the problems with detergents
- Take much longer to break down than spas. This leads to foam forming in rivers etc
- Can irritate and dry out skin
What happens when water and oil mixes
They will form an emulsion
What do emulsifiers do
addition of an emulsifier allows two otherwise immiscible layers to be mixed uniformly, dispersing an equal amount of each throughout the entire volume. The mixture is able to exist as a stable (non-separating) emulsion for a reasonable time (known as shelf-life)
