Carboxylic acids and esters

Question 1

What do carboxylic acids react to form?

Answer 1

React with carbonates to form a salt, water and carbon dioxide

Question 2

What do carboxylic acids form when dissociated partially?

Answer 2

H+ and carboxylate ion (equilibrium lies to the left)

Question 3

How are esters made?

Answer 3

Reacting alcohols with carboxylic acids or acid anhydrides

Question 4

What is the functional group of an ester?

Answer 4

-COO-

Question 5

What catalysts are used in esterification?

Answer 5

Sulfuric acid catalyst

Question 6

What happens when an acid anhydride reacts with alcohol?

Answer 6

An ester and carboxylic acid are formed

Question 7

Where are esters used?

Answer 7

• Perfumes
• Food flavourings

Question 8

How are esters used as solvents?

Answer 8

• They are polar, so other polar compounds will dissolve readily in them
• They also have low boiling points so will evaporate easily

Question 9

How are esters used as plasticisers?

Answer 9

They can be added to make plastics more flexible during the polymerisation process

Question 10

How can ester hydrolysis be sped up?

Answer 10

Using either an acid (acid hydrolysis) or a base (base hydrolysis)

Question 11

What is acid hydrolysis?

Answer 11

A dilute acid is used to split an ester into a carboxylic acid and an alcohol

Question 12

What acids are used in acid hydrolysis?

Answer 12

Sulfuric or hydrochloric acid

Question 13

How is an acid hydrolysis reaction conducted?

Answer 13

Under reflux

Question 14

What is base hydrolysis?

Answer 14

A dilute base is used to split an ester into a carboxylate ion and an alcohol

Question 15

What base can be used in base hydrolysis?

Answer 15

Sodium hydroxide

Question 16

How is a base hydrolysis reaction conducted?

Answer 16

Under reflux

Question 17

What is produced when glycerol (alcohol) and fatty acids (carboxylic acids) react?

Answer 17

Produces an ester which makes fats and oils

Question 18

What is a saturated fatty acid?

Answer 18

Contains no C=C in fatty acid tails

Question 19

What is an unsaturated fatty acid?

Answer 19

Contains one or more C=C in fatty acid tails

Question 20

Why do unsaturated fatty acids (oils) have lower melting points?

Answer 20

• The hydrocarbon chains are not straight
• The chains cannot pack closely together
• Van der Waal’s forces are weaker
• Liquid at room temperature

Question 21

Why do saturated fatty acids (fats) have higher boiling points?

Answer 21

• The hydrocarbon chains are straight and uniform
• The chains can pack together closely
• Stronger Van der Waal’s forces
• Solids at room temperature

Question 22

How is soap formed?

Answer 22

When fats or oils are hydrolysed by heating with NaOH

Question 23

How is biodiesel made?

Answer 23

Vegetable oils reacted with methanol and a KOH catalyst

Question 24

What does the reaction of the oil and methanol form?

Answer 24

Biodiesel (methyl ester) and glycerol

Question 25

What is the functional group of acyl chlorides?

Answer 25

-COCl

Question 26

What can acyl chlorides react with?

Answer 26

- Water - Ammonia - Alcohol - Primary amines In these, the Cl is substituted for either oxygen or nitrogen

Question 27

What happens when an acyl chloride reacts with water?

Answer 27

- Carboxylic acid and HCl formed - Vigorous reaction - White misty fumes of HCl gas

Question 28

What happens when an acyl chloride reacts with ammonia?

Answer 28

- Amide and HCl formed - Vigorous reaction - White misty fumes of HCl gas

Question 29

What happens when an acyl chloride reacts with alcohol?

Answer 29

- Ester and HCl formed - Vigorous reaction - White misty fumes of HCl gas

Question 30

What happens when an acyl chloride reacts with primary amines?

Answer 30

- N-substituted amides and HCl - Vigorous reaction - White misty fumes of HCl gas

Question 31

What is an acid anhydride?

Answer 31

A molecule made from two carboxylic acids that are the same

Question 32

What can acid anhydrides react with?

Answer 32

- Water - Ammonia - Alcohol - Primary amines

Question 33

How do acid anhydrides differ to acyl chlorides in their reactions?

Answer 33

Acid anhydrides react less vigorously

Question 34

What happens when an acid anhydride reacts with water?

Answer 34

Two carboxylic acids are formed

Question 35

What happens when an acid anhydride reacts with ammonia?

Answer 35

An amide and carboxylic acid are formed

Question 36

What happens when an acid anhydride reacts with alcohol?

Answer 36

An ester and carboxylic acid are produced

Question 37

What happens when an acid anhydride reacts with a primary amine

Answer 37

An N-substituted amide and carboxylic acid are produced

Question 38

What mechanism is involved in the reaction of an acyl chloride?

Answer 38

Nucleophilic addition-elimination

Question 39

How is aspirin made?

Answer 39

By adding either ethanoic anhydride or ethanoyl chloride with salicylic acid

Question 40

What else is produced in the making of aspirin?

Answer 40

Ethanoic acid

Question 41

Why is ethanoic anhydride used as opposed to ethanoyl chloride?

Answer 41

- It is less corrosive - It is cheaper - Does not produce HCl gas - Does not react vigorously with water

Question 42

What happens during recrystallisation?

Answer 42

1. Add hot solvent to allow the impure solid to dissolve, giving you a saturated solution 2. Allow solution to cool down and crystals will begin to form 3. Impurities will remain dissolved in the solution 4. Filter to get solid purified crystals and wash with very cold solvent 5. Dry crystals off

Question 43

How can you determine purity by boiling points?

Answer 43

1. Set up distillation equipment 2. Heat sample and measure temp. it evaporates 3. Compare boiling point to data book value 4. If boiling point higher or is over range of values, likely impure

Question 44

How can you determine purity by melting points?

Answer 44

1. Put sample in capillary tube and place in heating element of apparatus 2. Slowly increase temp. until sample begins melting 3. Record range from when starts to melt until fully melted 4. Compare against data book values 5. If impure, melting point lower and larger range