2.4 esters, fats and oils

Question 1

What is the functional group of an ester?

Answer 1

ester link

-COO-

Question 2

What are 3 uses of esters?

Answer 2

• flavourings
• fragrances
• solvents for non-polar compounds that do not dissolve in water

Question 3

What reaction forms an ester and what are the reactants?

Answer 3

condensation reaction between an alcohol and a carboxylic acid

Question 4

What is a condensation reaction?

Answer 4

two molecules are joined together with the elimination of a small molecule

Question 5

When an ester is formed by the reaction between a hydroxyl group and a carboxyl group, what small molecule is eliminated?

Answer 5

water

Question 6

What can esters be hydrolysed to produce?

Answer 6

an alcohol and a carboxylic acid

Question 7

What is a hydrolysis reaction?

Answer 7

a molecule reacts with water to break down into smaller molecules.

Question 8

What family are edible fats and edible oils a part of?

Answer 8

esters

Question 9

What is the systematic name for glycerol?

Answer 9

propane-1,2,3-triol

Question 10

How are edible fats and edible oils formed?

Answer 10

formed in the condensation reaction of glycerol and three fatty acid molecules

Question 11

What are long carbon chain, straight chain carboxylic acids called?

Answer 11

fatty acids

-they can be saturated or unsaturated

Question 12

What is the difference is melting points of edible oils and edible fats?

Answer 12

edible oils have lower melting points than edible fats

Question 13

Why do edible oils have lower melting points than edible fats?

Answer 13

• double bonds in fatty acid chains prevent oil molecules from packing closely together
• the greater the number of double bonds present, the weaker the London dispersion forces
• the greater the degree of unsaturation, the lower the melting point

Question 14

How do you test for unsaturated compounds and how does it work?

Answer 14

• unsaturated compounds quickly decolourise bromine solution
• the bromine molecules add across the carbon-carbon double bonds in an addition reaction
• oils with a higher degree of unsaturation will require a higher volume of bromine solution than oils with a lower degree of unsaturation

Question 15

Name 2 reasons why fats and oils are important

Answer 15

• they are a concentrated source of energy

- essential for the transport and storage of fat-soluble vitamins in the body (due to their non-polar structure)

Question 16

What is produced in the hydrolysis of edible fats and oils?

Answer 16

• 3 fatty acid molecules

- 1 glycerol molecule

Question 17

Will fats or oils decolourise bromine solution?

Answer 17

oils as they are unsaturated molecules

Question 18

How are esters named?

Answer 18

-the first part of the name which ends in -yl comes from the alcohol
-the second part of the name which ends in -oate comes from the acid
ethanol+methanoic acid
–>ethyl methanoate

Question 19

Why do esters have a lower boiling point than carboxylic acids and alcohols and why can they not dissolve in water?

Answer 19

they do not contain a hydroxyl group. therefore esters cannot form hydrogen bonds to neighbouring ester molecules

• less energy needed to separate molecules
• non polar

Question 20

What type of ester are edible fats and edible oils?

Answer 20

triester

-containing three ester links

Question 21

Why is glycerol so viscous and have a high boiling point compared to other alcohols?

Answer 21

• it has three -OH groups

- allows the glycerol molecules to form more hydrogen bonds between molecules than alcohols with only a single -OH group

Question 22

explain the difference between how fats are formed and how oils are formed?

Answer 22

• fats are formed from saturated fatty acids

- oils are formed from unsaturated fatty acids

Question 23

What is another name for fats and oils?

Answer 23

triglyceride

Question 24

Explain the packing of edible fats

Answer 24

• the efficient packing
• allows for the London dispersion forces to hold the fat molecules together
• these are greater between fat molecules than between oil molecules because of this efficient packing.
• this means that it will take more energy to separate fat molecules and so the melting point will be higher than oils
• solid at room temperature

Question 25

Explain the packing of edible oils

Answer 25

• the double bonds cause the molecules to have a distorted structure, which makes it difficult for them to pack closely together
• this results in fewer London dispersion forces between oil molecules
• it therefore takes less energy to break apart the oil molecules
• meaning that oils have a lower melting point than fats

Question 26

What is the catalyst used when producing an ester?

Answer 26

concentrated sufuric acid

Question 27

What is formed during the hydrolysis of an ester?

Answer 27

alcohol + carboxylic acid

Question 28

What are 2 observations that would show you have an ester?

Answer 28

• layers

- smell

Question 29

Where does an ester link break during hydrolysis?

Answer 29

between the carbon of the carboxylic acid and the oxygen

• H is added to the alcohol
• OH is added to the carboxylic acid

Question 30

Fats and oils belong to which family of compounds?

Answer 30

esters

Question 31

What is the catalyst used during esterification?

Answer 31

concentrated sulphuric acid

Question 32

why would you use a condenser during esterification?

Answer 32

to condense any vapours or reactants/products which evaporate