17C: Carboxylic acids

Question 1

Identify the functional group.

Answer 1

Carboxylic acid

Question 2

Explain the boiling temperatures of carboxylic acids.

Answer 2

Relatively high boiling point,
because molecules can form dimers with 2 H-bonds between each molecule.

Question 3

Explain the solubility of carboxylic acids.

Answer 3

Relatively high solubility,
because molecules can form H-bonds with water.

Question 4

State 2 methods of preparing carboxylic acids.

Answer 4

Oxidation of primary alcohols or aldehydes.

Hydrolysis of nitriles.

Question 5

Describe how to prepare carboxylic acids from primary alcohols or aldehydes

Answer 5

Acidified potassium dichromate.

Question 6

Describe how to prepare carboxylic acids from nitriles.

Answer 6

Acid hydrolysis: H₂O, dilute HCl

Alkali hydrolysis: H₂O, dilute NaOH
+ HCl to liberate parent acid of salt produced

Question 7

Reaction of carboxylic acids with lithium tetrahydridoaluminate:
Type of reaction,
Condition,
Product.

Answer 7

Reduction,
In dry ether,
Primary alcohol

Question 8

Describe the reaction:
Carboxylic acid -> Primary alcohol

Answer 8

React with LiAlH₄ in dry ether.

Question 9

Reaction of carboxylic acids with metal oxides/hydroxides:
Products.

Answer 9

Carboxylate salt, water

Question 10

Reaction of carboxylic acids with metal carbonates:
Products,
Observation.

Answer 10

Carboxylate salt, water, carbon dioxide,
Effervesence - turns limewater cloudy

Question 11

Describe the reactions:
Carboxylic acid -> Carboxylate salt

Answer 11

React with base,
e.g. Metal oxide, Metal hydroxide, Metal Carbonate.

Question 12

Test for carboxyl group.

Answer 12

React with Metal Carbonate,
CO₂ gas produced.

Question 13

Reaction of carboxylic acids with phosphorus(V) chloride:
Prodcuts,
Observation.

Answer 13

Acyl chloride, POCl₃, HCl,
Steamy white fumes - turns damp blue litmus red

Question 14

Describe the reaction:
Carboxylic acid -> Acyl chloride

Answer 14

React with PCl₅,
Produces POCl₃ and HCl,
Steamy white fumes

Question 15

Reaction of carboxlic acids with alcohols:
Condition,
Product.

Answer 15

Concentrated H₂SO₄ catalyst,
Ester

Question 16

Describe the reaction:
Carboxylic acid -> Ester

Answer 16

React with alcohol in conc H₂SO₄,
Equilibrium reaction.

Question 17

Identify the functional group.

Answer 17

Acyl chloride

Question 18

Identify the functional group.

Answer 18

Ester

Question 19

Reaction of acyl chlorides with water:
Products,
Observation

Answer 19

Carboxylic acid, HCl,
Steamy white fumes - turns damp blue litmus red

Question 20

Describe the reaction:
Acyl chloride -> Carboxylic acid

Answer 20

React with water,
Produces HCl,
Steamy white fumes

Question 21

Reaction of acyl chlorides with alcohols:
Products,
Observation.

Answer 21

Ester, HCl,
Steamy white fumes - turns damp blue litmus red

Question 22

Describe the reaction:
Acyl chloride -> Ester

Answer 22

React with alcohol,
Produces HCl,
Steamy white fumes

Question 23

Reaction of acyl chlorides with ammonia:
Condition,
Products

Answer 23

Concentrated NH₃,
Primary amide + ammonium chloride

Question 24

Describe the reaction:
Acyl chloride -> Primary amide

Answer 24

React with concentrated ammonia,
Produces ammonium chloride

Question 25

Reaction of acyl chlorides with amines:
Products

Answer 25

Secondary amide, quarternary ammonium chloride

Question 26

Describe the reaction:
Acyl chloride -> Secondary amide

Answer 26

React with amines,
Produces quarternary ammonium chloride

Question 27

Describe the hydrolysis of esters.

Answer 27

Acid hydrolysis: H₂O, dilute HCl

Alkali hydrolysis: H₂O, dilute NaOH
+ HCl to liberate parent acid of salt produced

Question 28

State 3 methods of producing polyesters.

Answer 28

Dicarboxylic acid + Diol
Diacyl chloride + Diol
Hydroxycarboxylic acid