Section E Flashcards
What is a soap?
A sodium salt of fatty acid
Name a common soap
Sodium stearate
Describe the ‘tail’ involved
Long, non-polar tail of hydrophobic nature being readily soluble in non-polar compounds
Describe the ‘head’ involved
Ionic carboxylate head that is negatively charged of hydrophilic nature being soluble in water
What type of reaction is used to produce soap?
Hydrolysis
Explain the process of making a soap from a fat or oil
The fat is hydrolysed to form fatty acids and glycerol. The sodium hydroxide then neutralises the fatty acids to produce a water soluble ionic salt called a soap
What is a soap used for?
Cleaning skin and removing non-polar substances like oil and grease
What does hydrolysis of fats and oils always produce?
Three fatty acid molecules and one glycerol molecule
What happens with soap when mixed with hard water?
Hard water contains high levels of dissolved metal ions which react with water to form scum, an insoluble precipitate
What is an advantage of using soapless detergents?
They don’t produce scum
Describe how soap works
Soaps and detergents dissolve in water and ionise to form negative soap ions and the hydrophobic tails of the ions dissolve in the droplet and the hydrophilic heads face out into the surrounding water. Aggravation of the mixture results in ball-like structures forming and these break up to form smaller droplets still with the hydrophilic heads on the outside and hydrophobic tails on the inside. Repulsion between the negative hydrophilic head of these droplets results in an emulsion being formed and the oil and grease being kept suspended in the water.
What is an emulsion?
An emulsion is small droplets if one liquid suspended in another liquid
What are emulsions in food?
Mixture of water and oil e.g. mayonnaise, sauces, ice cream, low fat spread
What happens when a non-polar and a polar liquid mix?
They quickly separate into two layers
How do you prevent a non-polar and polar mixture separating?
Adding an emulsifier
