2A Esters, Fats & Oils

Question 1

Why are oils liquid?
Explain fully.

Answer 1

Oils are made using mostly unsaturated fatty acids that cannot pack closely together, as C=C bonds present distort chains.
= decreased ldf forces (intermolecular forces).
= less energy being required to separate the oil molecules.
= mpt/bpt’s are lower than fats.

Question 2

Alcohol reacting with carboxylic acid to produce an ester is an example of what type of chemical reaction.

Answer 2

Condensation (and esterification).

Question 3

What sort of acids are used to produce fats/oils?

Answer 3

Long, chain fatty acids.
Fatty carboxylic acids.

Question 4

Natural fats and oils can be classified according to their origin.
Give 3 examples of where fats/oils can be found naturally.

Answer 4

Plant
Animal
Marine

Question 5

How many hydroxyl groups are present in glycerol?

Answer 5

3
Glycerol is a trihydritic alcohol.
Glycerol is a triol.

Question 6

True of false?
“Fatty acids can be saturated.”

Answer 6

True.
e.g. C17H35COOH = Saturated fatty acid.
The number of H is twice the number of C (2 x 17 = 35), so only C-C single bonds present.

Question 7

State 2 uses of esters.

Answer 7

1. Solvent.
2. Flavouring.

Question 8

Give two pieces of evidence that show an ester has been formed in esterification.

Answer 8

1. Oily layer on top of the water.
2. Characteristic ester smell.

Question 9

Esters are produced when which two substances react together?

Answer 9

1. Alcohol
2. Carboxylic acid

Question 10

What is the chemical name for a fat or oil (i.e. an ester of glycerol and three fatty acid molecules)?

Answer 10

Triglyceride

Question 11

How many moles of fatty acid reacts with 1 mole of glycerol, when a fat/oil is produced in a condensation reaction?

Answer 11

3 moles of fatty acid react with 1 mole of glycerol.

Question 12

What is a hydrolysis reaction?

Answer 12

The chemical breakdown of a molecule by reaction with water.

Question 13

True of false?
“Fatty acids can be saturated.”

Answer 13

True.
e.g. C17H33COOH = Unsaturated fatty acid.
The number of H is NOT twice the number of C (2 x 17 = 35 and there are only 33), so ONE C=C double bond present.
For every 2 H atoms “missing” this identifies ONE C=C bond.

Question 14

Why is a wet paper towel wrapped around the top of the test tube used for an esterification reaction?

Answer 14

To act as a condenser, to stop the escape of products from test tube.

Question 15

Why is a cotton wool plug used in the opening of the test tube used for an esterification reaction?

Answer 15

To stop hot acid escaping from the test tube.

Question 16

What family of chemical compounds do fats/oils belong to?

Answer 16

Esters

Question 17

Name a “reversible” chemical reaction.

Answer 17

Esterification.

Question 18

Methanoic acid and hexanol produce which ester?

Answer 18

Hexyl methanoate.

Question 19

Butanol and ethanoic acid would produce which ester?

Answer 19

Butyl ethanoate

Question 20

State two properties of esters.

Answer 20

1. Insoluble in water.
2. Characteristic smell.

Question 21

How many moles of water are produced when a fatty acid is produced in a condensation reaction?

Answer 21

3 moles of water produced. One for each ester link formed.

Question 22

What is a condensation reaction?

Answer 22

When two molecules react together to produce one larger molecule with loss of water.

Question 23

Why are fats/oils essential for humans?

Answer 23

For the transport and storage of fat soluble vitamins in the body.

Question 24

Why are fats solid?
Explain fully.

Answer 24

Fats are made using mostly saturated fatty acids. These acids can pack closely together.
= increased ldf forces (intermolecular forces).
= more energy being required to separate the fat molecules.
= mpt/bpt’s are higher than oils.

Question 25

Methyl pentanoate was formed from which alcohol and carboxylic acid?

Answer 25

Methanol
Pentanoic acid

Question 26

Name the alcohol used to make fats/oils.

Answer 26

Glycerol
Propan-1,2,3-triol

Question 27

Why is the esterification reaction mixture poured into a beaker containing an aqueous solution of sodium hydrogencarbonate?

Answer 27

To neutralise the sulfuric acid and obtain the ester.

Question 28

Why is concentrated sulfuric acid used in an esterification reaction?

Answer 28

Conc. sulfuric acid acts as a catalyst in an esterification reaction.
It also acts as a dehydrating agent (it removes water) to help prevent the reverse reaction from taking place.