6.1.3 Carboxylic Acids and Esters

Question 1

What is the functional group for a carboxylic acid

Answer 1

-COOH

Question 2

What suffix is used when naming carboxylic acids?

Answer 2

-oic acid

Question 3

How would you name CH3CH2CH2COOH

Answer 3

butanoic acid

Question 4

How can you synthesise carboxylic acids

Answer 4

By oxidation of a primary alcohol or aldehyde with acidified potassium dichromate. The reactants should be heated under reflux.

Question 5

How can a carboxylic acid be synthesised from a nitrile?

Answer 5

By hydrolysis

Question 6

Explain the solubility of carboxylic acids

Answer 6

The COOH functional group can form hydrogen bonds with water so shorter chain carboxylic acids are soluble.

Question 7

Explain the melting points of carboxylic acids compared to their equivalent alkanes

Answer 7

Carboxylic acids have higher melting points than their equivalent alkanes because they can form hydrogen bonds between molecules which require more energy to overcome than the weaker London forces in alkanes.

Question 8

How does a hydrogen bond occur?

Answer 8

The lone pair on F,O or N forms an attraction to a H atom attached to F, O or N.

Question 9

Why are carboxylic acids weak acids. Use the example of ethanoic acid.

Answer 9

They partially dissociate in water.

CH3COOH CH3COO- + H+

Question 10

Give 4 reactions of carboxylic acids

Answer 10

Neutralisation:
1. acid + alkali --> salt + water
2. acid + base --> salt + water
3. acid + metal carbonate --> salt + water + carbon dioxide
Redox:
4. Acid + metal --> salt + hydrogen

Question 11

Write the equation for the reaction of ethanoic acid with sodium hydroxide

Answer 11

CH3COOH + NaOH –> CH3COONa + H2O

Question 12

Write the equation for the reaction of ethanoic acid with magnesium

Answer 12

2CH3COOH + Mg –> (CH3COO)2Mg + H2

Question 13

Write the equation for the reaction of ethanoic acid with calcium oxide

Answer 13

2CH3COOH + CaO –> (CH3COO)2Ca + H2O

Question 14

Write the equation for the reaction of ethanoic acid with sodium carbonate

Answer 14

CH3COOH + Na2CO3 –> CH3COONa + H2O + CO2

Question 15

How can you test for a carboxylic acid

Answer 15

Add sodium carbonate. If there is effervescence then it is an acid. (This assume you know it is an organic compound so won’t be any other type of acid)

Question 16

What would you name the organic ion formed from a carboxylic acid

Answer 16

carboxylate ion

Question 17

How would you name CH3COONa

Answer 17

sodium ethanoate

Question 18

How would you name CH3COOCH3

Answer 18

methyl ethanoate

Question 19

What conditions are needed to form an ester from a carboxylic acid?

Answer 19

alcohol
concentrated sulfuric acid catalyst
heat under reflux

Question 20

What is the name of the reaction between a carboxylic acid and an alcohol

Answer 20

esterification

Question 21

What are the uses of esters

Answer 21

perfumes and food flavourings (they smell sweet and have low bps)
solvents for polar molecules

Question 22

What 3 compounds could be reacted with an alcohol to make an ester. Compare the 3

Answer 22

1. carboxylic acid
2. acid anhydride
3. acyl chloride
   The reaction with carboxylic acid is slower and doesn’t go to completion.
   The reaction with acyl chloride is fastest but produces toxic HCl as the byproduct.
   The reaction with acid anhydride is slower than with acyl chloride but faster than carboxylic acid. The second product is a carboxylic acid which can also react with the alcohol to produce more product.

Question 23

What is the name of the mechanism for the reaction between acid anhydride and alcohol

Answer 23

nucleophilic addition-elimination