soaps, detergents and emulsions Flashcards
How are soaps formed?
Alkali hydrolysis of fats and oils.
In the presence of alkali, a water soluble ionic salt is produced of the carboxylic acid through the neutralisation of the fatty acid molecules. These salts are soaps.
What are detergents?
Substances with non-polar hydrocarbon tails and ionic hydrophilic heads which remove oil and grease in the same way as soap and do not form a scum in hard water.
Why are soaps and detergents used to remove grease?
Since fats and oils are non-polar compounds they do not dissolve in water, soaps and detergents act as ‘emulsifying agents’ to allow oil and water to mix and produce stable emulsion.
Chemistry behind soap…
Soap ions have long non-polar tail which is soluble in non-polar compounds (hydrophobic) such as grease.
The ionic carboxylate head is water soluble (hydrophilic).
How does soap work?
Hydrophobic tails dissolve in grease while hydrophilic head faces outwards to surrounding water resulting in ball like structures called micelles.
Agitation causes micelles to form which are negatively charged and repel each other so grease suspended in water.
What is hard water?
Describes water containing high levels of dissolved metal ions.
What is scum?
An insoluble precipitate formed by using soap in hard water, can be avoided by using soapless detergents instead.
What is an emulsion?
An emulsion contains small droplets of one liquid dispersed in another liquid.
e.g. grease and soap suspended in water, soap is the emulsifier
What is an emulsifier for?
Soap-like molecule used to prevent oil (non polar) and water (polar) components separating into layers.
How are emulsifiers made?
In food, emulsifiers are made by reacting edible oils with glycerol
Emulsifier structure…
Only one or two fatty acids linked to each glycerol backbone. The 1/2 hydroxyl groups are hydrophilic and the fatty acids are hydrophobic.
How do emulsifiers work?
Acts like a soap to allow oil to disperse in water.
Fatty acid chains dissolve in oil while hydroxyl groups dissolve in water to form a stable emulsion.
Foods that contain emulsions…
Mayonnaise - mainly vegetable oil and water/vinegar/lemon using egg yolk as an emulsifier.
Examples of emulsifiers (don’t think this is needed but oh well)
Egg yolk, glycerol, agar, mustar, soaps
