11. Esters (including Fats and Oils)

Question 1

What are the reactants to make esters?

Answer 1

Carboxylic acids and alkanols

Question 2

What type of reaction is esterification?

Answer 2

Condensation

Question 3

What catalyst is used in reaction mixture?

Answer 3

Concentrated sulphuric acid

Question 4

Why is a water bath used to heat mixture?

Answer 4

Alkanols are flammable

Question 5

What is purpose of small test tube?

Answer 5

Acts as a condenser

Question 6

What are sources of fats and oils

Answer 6

Question 7

What category of compounds are fats and oils?

Answer 7

They are esters

Question 8

Why are fats and oils sometimes called tri-esters?

Answer 8

Because they have 3 carboxylate (ester link) groups in each molecule

Question 9

What is the parent alkanol in all fats and oils?

Answer 9

Glycerol

Propan-1, 2, 3 triol

Question 10

What is the structure of glycerol?

Answer 10

Question 11

What is meant by a fatty acid?

Answer 11

A long chain carboxylic acid with a 16 or 18 carbon chain

Question 12

What is the ratio of fatty acid to glycerol molecules when a fat or oil is made?

Answer 12

3:1

Question 13

What are the differences between fats and oils?

Answer 13

Question 14

What is meant by an “unsaturated” molecule?

Answer 14

A molecule with at least 1 C=C bond present

Question 15

Testing fats and oils for levels of unsaturation

Answer 15

Also see video on google classroom

Question 16

What effect does unsaturation have on the shape of tri-esters?

Answer 16

Question 17

What effect does the irregular shape of unsaturated “tuning fork” have on how the molecules pack together?

Answer 17

Question 18

How could the levels of unsaturation in oils / fats be tested?

Answer 18

Bromine (or Iodine) will add across the C=C bond and decolourise as it does so.

A clear end point will be shown when the decolourising stops.

The more C=C bonds there are, the higher the volume of Br₂ or I₂ it will take to reach end point

Question 19

Tri-esters are also known as what (based on glycerol name)

Answer 19

Tri-glycerides

Question 20

Why are some oils hydrogenated?

Answer 20

To make them have higher melting points and be more stable.

Question 21

What are the 6 points needed to be covered to explain difference in melting points of fats and oils?

Answer 21

1. Level of unsaturation (C=C bonds)
2. Effect this has on tuning fork shape
3. Effect this has on how close they can pack together
4. Effect this has on intermoleular (LDF) attractions
5. Level of energy need to break them
6. corresponding lower or higher melting point

Question 22

What happens to fats and oils when they react with oxygen?

Answer 22

They become rancid

Question 23

What is meant by “hydrolysis”?

Answer 23

The breaking down of a molecule using the chemical action of water

Question 24

Which molecule is ALWAYS produced when fats and oils are hydrolysed?

Answer 24

Glycerol

Question 25

Given that esters and carboxylic acids are isomers, how could we distinguish between them?

Answer 25

• pH indicator; acids -red; esters stay green
• electrical conductivity; only acids would conduct.
• solubility (miscibility) in water; only acids would be soluble (miscible)
• reaction with Mg. Only acids would react to release hydrogen.
• smell: esters would (mostly) have a sweet smell where acids would be sour or sharp