Natural fats and oils

Question 1

What are fats and oils?

Answer 1

Fats and oils are all part of a group of compounds called esters. They all have chains of carbon atoms.

Question 2

Saturation

Answer 2

• If the carbon chain contains only single carbon-carbon bonds, the fat is saturated.
• If the carbon chain contains some double carbon-carbon bonds then the oil unsaturated.

Question 4

Unsaturation test

Answer 4

• To test for unsaturation the oil is shaken with bromine water, which is orange.
• Unsaturated compounds loose their colour decolorise.
• The colour remains orange with saturated compounds.

Question 5

Vegetable oils are:

Answer 5

unsaturated

Question 6

One industrial use of vegetable oils is to make margarine.

Answer 6

• The first stage is to ‘harden’ the oils, turning them into saturated compounds.
• Hydrogen is bubbled through the oil at about 200 ºC using a nickel catalyst.
• The hydrogen reacts with the carbon-carbon double bonds and turns them into single bonds.

Question 7

Where do saturated fats and oils come from?

Answer 7

• Saturated fats and oils usually come from animals and unsaturated fats and oils usually come from plants.
• ‘Polyunsaturated’ means the compound contains more than one carbon-carbon double bond.
• People whose diet is rich in unsaturated fats and oils have lower levels of the type of cholesterol that causes heart diseases.

Question 8

Getting fats into water

Answer 8

• Oil and water are immiscible liquids. They do not dissolve in each other, but disperse into tiny droplets to form an emulsion.
• Milk is an oil-in-water emulsion.
• Cold cream and margarine are water-in-oil emulsions.

Question 9

What is bromine?

Answer 9

• Bromine is an orange liquid. Bromine reacts, in an addition reaction, with the carbon-carbon bonds in the chain.
• The reaction uses up the bromine molecules, making a dibromo compound. This compound is colourless.
• Saturated compounds cannot react with bromine since they have no carbon-carbon double bond.

Question 11

Saponification

Answer 11

• Fats and oils can be split up using hot sodium hydroxide to make soap and glycerol.
• The reaction of splitting up natural oils with alkalis is called saponification.

Question 12

When an ester reacts with sodium hydroxide

Answer 12

• Saponification occurs.
• This ester forms one glycerol molecule and three soap molecules.
• This reaction is really the reaction of alkaline water so it is a hydrolysis reaction. The reaction is:
• fat + water ⇒ soap + glycerol