Carboxylic acids and derivatives

Question 1

=carboxylic acid groups on both ends of the chain

Answer 1

• dioic acid
  keep ‘e’
  eg. ethanedioic acid

Question 2

acidity

Answer 2

The carboxylic acid are only weak acids in water and only slightly dissociate, but they are strong enough to displace carbon dioxide from carbonates.

Question 3

solubility

Answer 3

The smaller carboxylic (up to C4) acids dissolve in water in all proportions but after this the solubility rapidly reduces. They dissolve becausetheycanhydrogenbondto the water molecules.

Question 4

delocalisation

Answer 4

The carboxylic acid salts are stabilised by delocalisation, which makes the dissociation more likely.

Question 5

alkyl groups: delocalisation

Answer 5

Increasing chain length pushes electron density on to the COO- ion, making it more negative and less stable. This make the acid less strong.

Question 6

chlorine: delocalisation

Answer 6

Electronegative chlorine atoms withdraw- electron density from the COO ion, making it less negative and more stable. This make the acid more strong.

Question 7

oxidation of methanoic acid

Answer 7

Carboxylic acids cannot be oxidised by using oxidising agents but methanoic acid is an exception as its structure has effectively an aldehyde group

Question 8

esterification

Answer 8

Carboxylic acids react with alcohols, in the presence of a strong acid catalyst, to form esters and water.

Question 9

uses of esters

Answer 9

Esters are sweet smelling compounds that can be used in perfumes and flavourings.

Esters can be used as solvents for polar organic substances.
Ethyl ethanoate is used as a solvent in glues and printing inks.

plasticisers

Question 10

esters properties

Answer 10

For use in perfumes they need to be non toxic, soluble in solvent such as ethanol, volatile (turns into gas easily), and not react with water.
Although polar, they do not form hydrogen bonds (reason: there is no hydrogen bonded to a highly electronegative atom).
They have a lower b.p. than the hydrogen-bonded carboxylic acids they came from. They are also almost insoluble in water.
Often pure polymers have limited flexibility because the polymer chains cannot move over each other.
Incorporating some plasticiser into the polymer allows the chains to move more easily and the polymer can become more flexible.