Carboxylic Acids

Question 1

Carboxylic acid functional group

Answer 1

Carboxyl group - COOH.

Contains both hydroxyl and carbonyl group, the presence of both of these means carboxylic acids have there own group of chemical properties.

Both the OH and CO are polar, making the Carboxyl group super, duper polar! xD

Question 2

Making carboxylic acids

Answer 2

Carboxylic acids are made from the oxidation of primary alcohols or esters.

Can be oxidized by acidified potassium dichromate ions.

Question 3

Acid reaction of carboxylic acids

1) In water
2) Carbonate
3) Metal
4) OH- ion

Answer 3

1) Carb. acids are weak acids.They partially dissociate in water.
2) They react with cabonates to form a salt, CO2 and water. Fizzing is seen. Neatralisation reaction.
3) Salt and hydrogen. Neatralisation reaction.
4) Carboxylate ions. The lone pair of electrons on the oxygen atom and the pi electrons in the C=O bond form a delocalized system. This means the negative charge on the oxygen is delocalised and each carbon-oxygen bond is the same length and strength. This stabilizes the carboxylate ion and explanes why the carboxylate acids are acidic while alcohols, which cannot form delocalized structures, are neatrual

Question 4

Water solubilty of carboxylic acids

Answer 4

Short chains - very soluble

carb. acids contain C=O and O-H, both very polar. H-bonds form between them and the water molecules.

As the carbon chain length increase, the carb. acids become less soluble in water as the non-polar C chains do not interact with the water molecules.

Question 5

Naming esters

Answer 5

Part 1: Alcohol

Part 2: Carboxylic Acid

Question 6

Making esters

Answer 6

Esters are made in esterification reactions between carboxylic acids and alcohols in the presence of:

concentrated sulfuric acid or hydrochloric acid catalyst

reversible reaction

Question 7

The hydrolysis of esters

Answer 7

The reverse of an esterification reaction is called hydrolysis,

Hydrolysis is the breaking down of a compound using water.

The reaction can be carried out in a solution of a dilutre acid or dilute alkali

Hydrolysis using an alkali is the preferred method becuase the reaction happens more quickly. In this method, as the carboxylic acid is formed it reacts with the alkali to form the salt of the carboxylic acid.

Question 8

Useful esters:

Where are they found in nature?

What are they used for?

Answer 8

Esters are found in nature as oils and fats

They are usful compounds with pleasent fruity smells and are often used as synthetic food flavourings:
cheaper than using natural flavourings but some people can tase the difference

They are used as solvents in perfurmeds

They are used as plasticizers (chemicals that are added to plastics to make them softer and more flexible)