Carboxylic Acids and Derivatives

Question 1

describe how the addition of a halogen to a carboxylic acid changes its acidity

Answer 1

• the halogen is more electronegative and so attracts electron density towards itself
• this polarises the OH bond making it weaker
• therefore the H is more easily dissociated

Question 2

how do you test for carboxylic acids

Answer 2

• Sodium carbonate
• positive = effervescence

Question 3

how are esters made

Answer 3

• Esterification
• reaction between alcohol and carboxylic acid
• concentrated sulfuric acid catalyst

Question 4

what is esterification

Answer 4

• reaction between alcohol and carboxylic acid
• concentrated sulfuric acid catalyst

Question 5

what are some uses of esters

Answer 5

• flavourings
• perfumes
• plasticisers

Question 6

what is the functional group isomer of a carboxylic acid

Answer 6

esters

Question 7

how are esters hydrolysed?

Answer 7

• Acid Hydrolysis
• Basic Hydrolysis

Question 8

Describe the process of Acid Hydrolysis of Esters

Answer 8

• excess water and dilute H₂SO₄ catalyst added to Ester
• Ester is hydrolysed back into carboxylic acid and Alcohol
• reversible reaction

Question 9

Describe the process of Basic Hydrolysis of Esters

Answer 9

• ester is heated with alkali producing alcohol and carboxylate salt
• excess H₂SO₄ is added to the salt which reforms the carboxylic acid

Question 10

why may basic hydrolysis be preferred to acid hydrolysis when hydrolysing esters?

Answer 10

• acid hydrolysis is a reversible reaction and so it gives a low yield of carboxylic acid and alcohol

Question 11

describe the hydrolysis of fats

Answer 11

• triglycerides are hydrolysed using a hot NaOH/KOH solution to form glycerol and sodium/potassium carboxylate salts

Question 12

what is the use of carboxylate salts

Answer 12

• used in the manufacture of soaps

Question 13

what is the use of glycerol

Answer 13

• it is a useful solvent

Question 14

what is biodiesel

Answer 14

• liquid fuel consisting of a mixture of methyl esters of long chain carboxylic acids from vegetable oils

Question 15

describe how biodiesel is made

Answer 15

• triglyceride is reacted with methanol (CH₃OH) (with a strong acid catalyst) to form a mixture of methyl esters

Question 16

what is an acyl chloride?

Answer 16

• alcohol group of a carboxylic acid is replaced by a chlorine atom

Question 16

what is the mechanism for the acylation of alcohol. water and ammonia

Answer 16

• nucleophilic addition elimination

Question 17

why are acyl chlorides preferred to carboxylic acids in the formation of esters

Answer 17

• no acid catalyst is required
• purer product
• higher yield of ester as reaction isn’t reversible

Question 18

what are acyl chlorides used for

Answer 18

• the formation of esters (by reacting them with alcohols)
• the formation of carboxylic acids (by reacting them with water)
• the formation of n-substituted/amides (by reacting them with amines/ammonia)

Question 19

what are n-substituted amides

Answer 19

• an amide but one of the hydrogens on the ammonia has been replaced by a hydrocarbon group

Question 20

how to name n-substituted amides

Answer 20

• N-alkyl prefix (the carbons attached the N)
• anamide suffix (the carbons attached to the carbonyl group)

Question 21

why are acid anhydrides preferred to acyl chlorides when making esters

Answer 21

• acid anhydrides are less vulnerable to hydrolysis
• no corrosive HCl is formed

Question 22

what are the three methods of forming carboxylic acids

Answer 22

• oxidation of primary alcohols/aldehydes
• reaction of acyl chlorides with water
• reaction of acid anhydrides with water

Question 23

what are three methods of forming esters

Answer 23

• reaction of carboxylic acids with alcohol
• reaction of acyl chlorides with alcohol
• reaction of acid anhydrides with alcohol