Esters

Question 1

what needs to be reacted in order to make an ester ?

Answer 1

a carboxylic acid and an alcohol
- in the presence of sulphuric acid catalyst
- produces ester and water

Question 2

what is the process of making an ester called ?

Answer 2

• esterification

Question 3

describe the process of esterification ?

Answer 3

• the process is reversible and slow
• a conc acid us often used as a catalyst but is still a slow reaction

Question 4

how do you name esters ?

Answer 4

alcohol first, carboxylic acid second

e.g propyl methanoate

Question 5

what is the process of breaking down an ester back into a carboxylic acid and alcohol called ?

Answer 5

• ester hydrolysis

Question 6

what are the features of ester hydrolysis ?

Answer 6

• conc acid catalyst is used
• reversible reaction

Question 7

if an ester is reacted with an alkali, what happens ?

Answer 7

• it forms a salt of the carboxylic acid and an alcohol

Question 8

what is the process of reacting an ester with an alkali called ?

Answer 8

• saponification or base hydrolysis

Question 9

what are some uses of esters ?

Answer 9

• food additives / flavourings
• perfumes
• plasticisers
• glue

Question 10

what do many perfumes contain ?

Answer 10

• mixtures of esters in a solvent that quickly evaporates
• e.g ethanol

Question 11

what are plasticisers ?

Answer 11

• theses are added to polymers to make them more felxible

Question 12

what are the esters of propane-1,2,3-triol ?
(glycerol)

Answer 12

• vegetable oils
• animal fats

Question 13

what are examples of naturally occurring esters ?

Answer 13

• lipids (fats and oils )

Question 14

what is the structure of a lipid ?

Answer 14

3x fatty acids joined with a glycerol molecule

Question 15

what feature can the fatty acids have ?

Answer 15

• they can be either saturated or unsaturated

Question 16

what are lipids that are liquid at room temp called and what do they tend to be ?

Answer 16

• they are called oils
• tend to contain unsaturated fatty acids

Question 17

what are lipids that are solids at room temp called and what do they tend to be ?

Answer 17

• they are called fats
• tend to contain saturated fatty acids

Question 18

how are soaps most commonly made ?

Answer 18

• by boiling lipids with potassium hydroxide
• (acid hydrolysis)

Question 19

what does saponification using KOH produce ?

Answer 19

• 3x salts of fatty acids
• glycerol

Question 20

what is Biodiesel ?

Answer 20

• a mixture of methyl esters of long-chain carboxylic acids

Question 21

How is biodiesel produced ?

Answer 21

• Biodiesel is produced by reacting vegetable oils with methanol in the presence of a catalyst

Question 22

what is the process of making biodiesel called ?

Answer 22

• transesterification

Question 23

what occurs in transesterification ?

Answer 23

• the lipid is broken down into 3 fatty acids and glycerol by reaction with potassium hydroxide,
• then the fatty acids are converted into 3 new esters using methanol

Question 24

what does the potassium hydroxide act as and why ?

Answer 24

• the KOH is not used up and so acts as a catalyst