Carboxylic Acids

Question 1

Physical properties of Carboxylic acids

Answer 1

1) Colourless solution with sour taste

2) weak acid with pH

Question 2

Why does boiling point decrease with increase in branching?

Answer 2

Branching gives the molecules a more spherical shape leading to lower surface area for Van der Waal’s interaction and hence reduces Van der Waal’s forces between molecules.

Question 3

Why do Carboxylic acids have higher boiling points than corresponding alcohols of comparable molecular mass?

Answer 3

Each Carboxylic acid molecule contains a highly polar hydroxyl group which leads to 2 hydrogen bonds between two acid molecules compared to only one hydrogen bond between two alcohol molecules.

Question 4

Solubility in water of Carboxylic acids

Answer 4

Relatively soluble in water, solubility decreases with increase in molecular size

Solubility decreases as the length of the carbon chain increases, as the polar carboxyl group becomes and ever smaller part of the molecule and the molecule becomes more like a hydrocarbon

Question 5

Why does solubility of Carboxylic acids decrease at a slower rate than alcohols as molecular size increases?

Answer 5

• presence of carboxyl group enables each Carboxylic acid molecule to form 3 hydrogen bonds with water molecules in exothermic reaction
• with increase in length of carbon chain since carboxyl group can form 3 bonds it is less insignificant as hydroxyl group in alcohols

Question 6

Manufacture of Carboxylic acids

Answer 6

Same as two ways in which alcohols are oxidized. Carboxylic acids are formed from the oxidation of alcohols.

Question 7

What are the chemical properties of Carboxylic acids?

Answer 7

1) Same as acids- MASH, BASE and CASCW
2) Combustion (complete and incomplete)
3) Condensation Reaction (Name: Esterification)

Question 8

Diff between Carboxylic acids and regular acids

Answer 8

Carboxylic acids react less vigorously as they are weak acids and dissociate only partially in water to form hydrogen ions

Question 9

What is Esterification?

Answer 9

Carboxylic acids react with alcohols to form sweet smelling compounds called esters

Question 10

What are the conditions required for Esterification?

Answer 10

Heat under reflux, concentrated sulfuric acid as catalyst and dehydrating agent

Question 11

Diff between forward and backward reaction for Esterification

Answer 11

Forward reaction is condensation (evolves eg loses a water molecule)

Backward reaction is hydrolysis (uses water to form back ethanoic acid)

Question 12

For condensation reaction, which part is broken off th Carboxylic acid and alcohol?

Answer 12

Carboxylic acid: ALWAYS OH broken off

Alcohol: ALWAYS H broken off

Question 13

Why is concentrated sulfuric acid important as a dehydrating agent?

Answer 13

It is a strong dehydrating agent which pushes the equilibrium if the reaction forward to result in greater yield of esters by removing the water molecules as they are formed

Question 14

What are esters?

Answer 14

Esters are organic compounds with characteristic smells that are prepared by reacting alcohol using concentrated sulfuric acid as catalyst

Question 15

Compare the boiling points of esters with their corresponding Carboxylic acids with the same number of carbon atoms

Answer 15

Esters have lower boiling points than the corresponding Carboxylic acids with the same number of carbon atoms

Question 16

Why do esters have lower boiling points than Carboxylic acids with the same number of carbon atoms?

Answer 16

• due to absence of hydroxyl group, esters do not form hydrogen bonds between its molecules
• with only Van der Waal’s forces found between ester molecules, it is weaker than hydrogen bonding found between Carboxylic acid molecules

Question 17

Solubility of esters?

Answer 17

Esters are relatively soluble in water but decreases as molecular size increases

Question 18

Why are esters relatively soluble in water but decreases with increase in molecular size?

Answer 18

• hydrogen bonds are formed between ester and water molecules with partially positive hydrogen atoms in the water molecules attracted to lone pairs of oxygen atoms on the ester
• Hydrogen portion of the ester molecule force itself between the water molecules and break the relatively strong hydrogen bond as molecular size increases

Question 19

Uses of ethanoic acid

Answer 19

• food flavoring and preservative
• to make drugs such as aspirin
• bleaching agent in detergent

Question 20

Uses of citric acid

Answer 20

• natural preservative and anti-oxidant

- used in baking powder to react with sodium bicarbonate to result in the raising action from carbon dioxide formation

Question 21

Uses of esters

Answer 21

• To prepare cosmetics and perfumes
• artificial favour in processed food and drinks
• used in production of polyesters (synthetic fibers to make textiles)
• found naturally in fruits and flowers