Esters

Question 1

when are esters formed?

Answer 1

when a carboxylic acid reacts with an alcohol

Question 2

carboxylic acid + alcohol –> (reversible reaction)

Answer 2

ester + water

Question 3

condensation reaction

Answer 3

when two molecules join together with the elimination of water

Question 4

naming esters

Answer 4

1st part from alcohol add ‘yl’

2nd part from carboxylic acid add ‘oate’

Question 5

functional group of ester

Answer 5

ester linkage “coo” group

Question 6

hydrolysis

Answer 6

to split a molecule apart using water

Question 7

hydrolysis of esters

Answer 7

esters can be hydrolysed to their parent alcohol and carboxylic acid
ester linkage C-O bond is broken

Question 8

acid catalysed hydrolysis

Answer 8

H+ used as a catalyst
still reversible
will always get a mixture of ester, water, carboxylic aicd and alcohol

Question 9

alkali catalysed hydrolysis (“Alkaline Hydrolysis”)

Answer 9

if an alkali is used we get a complete hydrolysis of the ester (all ester hydrolysed)
forms carboxylic acid and alcohol but NaOH present so the carboxylic acid will react to form the salt

Question 10

final products of alkaline hydrolysis

Answer 10

salt of the carboxylic acid + alcohol

Question 11

method of making an ester

Answer 11

1. equal quantities of the reactants (alcohol and carboxylic acid) are added to a test tube
2. concentrated sulphuric acid is added as a catalyst
3. a wet paper towel is put around the top of the test tube to act as a condenser.
4. the tube is placed in a beaker of hot water/water bath.
5. reaction mixture is poured onto sodium hydrogen carbonate solution to neutralise the conc. sulphuric acid and any unreacted carboxylic acid

Question 12

why is the tube not heated with a bunsen?

Answer 12

Not heated with a bunsen since alcohols are flammable.

Question 13

evidence the ester has formed

Answer 13

1. distinct smell

2. two layers are formed (oily layer on top)

Question 14

main use of esters

Answer 14

flavouring and fragrances i.e. perfumes and deodorants

Question 15

examples of esters and their smells

Answer 15

methyl butanoate - pineapple
ethyl pentanoate - apple
benzyl ethanoate - peach, flowers

Question 16

why can esters be used as fragrances?

Answer 16

because they are volatile

Question 17

what is volatility?

Answer 17

the ease at which a substance evaporates i.e. l–>g

Question 18

what is volatility controlled by?

Answer 18

intermolecular bonds
stronger - less volatile
weaker - more volatile

Question 19

other uses of esters

Answer 19

industrial solvents (able to dissolve variety of compounds which are insoluble in water)
used as solvents for dyes, inks, paints and varnishes
used to extract caffeine from coffee/tea

Question 20

properties of esters

Answer 20

volatile
distinctive smells
flammable

Question 21

what catalyst is used when making esters?

Answer 21

concentrated sulfuric acid

Question 22

what does the wet paper towel act as when making an ester?

Answer 22

a condensor

Question 23

what is the opposite of a condensation reaction?

Answer 23

a hydrolysis reaction

Question 24

what is heating under reflux?

Answer 24

heating the mixture with a condenser attached

Question 25

what does heating under reflux ensure?

Answer 25

that volatile compounds do not escape and allows the reaction to take place at a higher temperature.

Question 26

what parts of the alcohol and carboxylic acid are removed to form water during esterification?

Answer 26

• a hydrogen atom is removed from the hydroxyl group of the alcohol
• the -OH part of the carboxylic acid’s carboxyl group is also removed.