6.1.3 - Carboxylic Acids and Esters

Question 1

Why are carboxylic acids soluble in water?

Answer 1

Due to the highly polarised d+ hydrogen and d- oxygen which form hydrogen bonds with water molecules.

Question 2

What do carboxylic acids form with water?

Answer 2

Dimers (both hydrogen and oxygen react with water)

Question 3

Why are longer hydrocarbon chain carboxylic acids less soluble in water?

Answer 3

The long chain is non-polar.

Question 4

Why aren’t hydrogen bonds in alcohols as strong as in carboxylic acids?

Answer 4

Carboxylic acids form dimers.

Question 5

What are carboxylic acids?

Answer 5

Weak acids.

Question 6

Acid + metal

Answer 6

metal salt + H2

Question 7

Acid + carbonate

Answer 7

metal salt + CO2 + H2O

Question 8

Acid + base

Answer 8

metal salt + H2O

Question 9

Test for hydrogen?

Answer 9

Lighted spill goes out with a squeaky pop.

Question 10

Test for water?

Answer 10

Cobalt chloride paper turns blue.

Question 11

Test for CO2?

Answer 11

Turns limewater cloudy.

Question 12

Functional group of esters?

Answer 12

-COO-

Question 13

How are esters formed in esterification?

Answer 13

By reacting carboxylic acids with an alcohol in the presence of a concentrated H2SO4 catalyst.

Question 14

What is the drawback of esterification?

Answer 14

Low yield as reaction is reversible so product must be separated using distillation as soon as it forms.

Question 15

How are esters named?

Answer 15

First part comes from the alcohol, second the acid.

Question 16

Methanoic acid + ethanol?

Answer 16

Ethyl methanoate

Question 17

How are acid anhydrides formed?

Answer 17

Two carboxylic acids react eliminating a water molecule.

Question 18

How are acid anhydrides used to form esters?

Answer 18

They are heated without a catalyst with an alcohol.

Question 19

What is produced when acid anhydrides form esters?

Answer 19

The ester and a carboxylic acid which must be separated by fractional distillation.

Question 20

Why does the formation of esters by acid anhydrides give a better yield?

Answer 20

The reaction is not reversible.

Question 21

What is the hydrolysis of esters?

Answer 21

A chemical reaction where water causes the breaking of bonds in a decomposition reaction.

Question 22

General equation for hydrolysis of esters?

Answer 22

ester + water -> carboxylic acid + alcohol

Question 23

What happens in acid hydrolysis?

Answer 23

Reflux the ester with the dilute sulphuric acid catalyst. This is a reversible reaction.

Question 24

What happens in alkali hydrolysis?

Answer 24

Reflux the ester with aqueous NaOH solution to form the alcohol and carboxylate salt of the acid.

Question 25

Why is alkali hydrolysis not reversible?

Answer 25

No acid is formed, only the salt.

Question 26

How are acyl chlorides formed?

Answer 26

Carboxylic acid + SOCl2 -> acyl chloride + SO2 + HCl

Question 27

How do you separate the byproducts from the acyl chloride in the formation of acyl chloride?

Answer 27

Distillation as although the byproducts are both gases there may be excess acid.

Question 28

How are carboxylic acids formed by acyl chlorides?

Answer 28

A nucleophilic substitution reaction with water.

acyl chloride + water -> carboxylic acid + hydrogen chloride

Question 29

How are esters from acyl chlorides, and why is it a good way of forming esters?

Answer 29

A nucleophilic addition reaction with an alcohol.

acyl chloride + alcohol -> ester + hydrogen chloride. Not a reversible reaction so should give a better yield.

Question 30

How are primary amides formed from acyl chlorides?

Answer 30

Reaction with ammonia.

acyl chloride + ammonia -> amide + hydrogen chloride (ammonium chloride if excess ammonia used)

Question 31

How are secondary amides formed from acyl chlorides?

Answer 31

Reaction with amines.

Acyl chloride + amine -> amide + hydrogen chloride