Soaps, detergents and emulsions

Question 1

Describe soap formation.

Answer 1

1. Soaps are produced by the alkaline hydrolysis of edible fats and oils.
2. This produces 3 fatty acid molecules and glycerol.
3. The fatty acid molecules are then neutralised by an alkali, forming ionic (water soluble) salts called soaps.

Question 2

Use of soaps.

Answer 2

Soaps are used to remove non-polar substances like grease and oil.

Question 3

How do soaps work.

Answer 3

1. Soaps have a polar, hydrophilic, ionic head and a non-polar, hydrophobic tail.
2. When in contact with oil and water, the hydrophobic tail will enter the oil, leaving the hydrophilic head in the water.
3. The oil/grease is then formed into small balls called micelles.
4. They are held in this suspension as the negative heads repel each other preventing them combining together.
   (tails must be drawn fully submerged in grease)

Question 4

What is hard water?

Answer 4

1. Water containing high levels of dissolved metal ions.
2. Scum (an insoluble precipitate) is commonly found in areas which have hard water.

Question 5

What are soapless detergents?

Answer 5

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

Question 6

What are emulsifiers?

Answer 6

1. Emulsifiers prevent non-polar and polar liquids separating into layers.
2. Emulsifiers have similar structures to fats and oils but have one or two fatty acid groups which can be added to glycerol.
3. While this forms an ester link with the glycerol there is still unused hydroxyl groups.
4. This means that there is a non-polar hydrophobic part which can dissolve in oil and a polar, hydrophilic (OH) group which can dissolve in water.