Soaps, Detergents and Emulsions

Question 1

How are soaps formed?

Answer 1

They are produced from the alkaline hydrolysis of edible fats and oils.
This hydrolysis produces 3 fatty acid molecules and glycerol.
The fatty acid molecules are then neutralised by an alkali, forming ionic salts (water soluble), which we call soaps.

Question 2

Use of soaps

Answer 2

to remove grease and oil (non-polar substances)

Question 3

How do soaps work?

Answer 3

Soaps have a polar, hydrophilic, ionic head and a non-polar, hydrophobic tail. When in contact with oil and water, the hydrophobic tail enters the oil and leaves the hydrophilic head in the water.
This makes the oil/grease form into small balls called micelles, they are held in suspension as the negatively charged heads repel each other preventing them from binding together.

Question 4

Hard water

Answer 4

This is water containing high levels of dissolved metal ions.
Scum (an insoluble precipitate) is commonly found in areas that have hard water.

Question 5

Soapless Detergents

Answer 5

These have non-polar hydrophobic tails and ionic hydrophilic ionic heads to remove oil and grease like normal soaps.
They do not form scum with hard water.

Question 6

Uses of emulsifiers

Answer 6

Emulsifiers prevent the non-polar and polar liquids separating into layers.

Question 7

How do emulsifiers work?

Answer 7

They have similar structures to fats and oils but have one or two fatty acid groups that can be added to glycerol.
This forms an ester link with the glycerol but still leaves unused hydroxyl groups.
This means that there is a non-polar hydrophobic part which can dissolves in oil, and there is a polar hydrophilic group which can dissolve in water.
Emulsifiers are used in food to stop oil and water from separating. (eg. mayo, milk, bread, sauces etc)