A Level Organic

Question 1

Carboxylic Acids

Answer 1

-Have -oic acid ending.
-Always at the end of the chain.
-Numbering always starts from carboxylic acid end.
-If there’s COOH on both sides, it is called a -dioic acid.

Question 2

Acidity of carboxylic acids

Answer 2

-Weak acids in water and only slightly dissociate.
-Strong enough to displace CO2 from carbonates.

Question 3

Solubility in water of carboxylic acids

Answer 3

-Smaller carboxylic acids dissolve in water in all proportions.
-Bigger chains have lower solubility.
-The dissolve easily because they can hydrogen bond to the water molecules.

Question 4

Delocalisation of carboxylic acids

Answer 4

-Salts are stabilised by delocalisation.
-Makes dissociation more likely.
-Have equal C-O bond lengths.
-Pi charge cloud delocalises and spreads out and makes ion more stable and more likely to form.

Question 5

Strength of carboxylic acids

Answer 5

-Increasing chain length pushes electron density on to the COO- ion.
-This makes it more negative and less stable- less strong.
-Electronegative chlorine atoms withdraw electron density from COO- ion.
-This makes it less negative and more stable- more strong.

Question 6

Carboxylic acid + Metal —>

Answer 6

Salt + Hydrogen
-Example- (CH3COOH + Na –> CH3COO-Na+ + 1/2 O2)

Question 7

Carboxylic acid + Alkali —>

Answer 7

-Salt + Water
-Example- (CH3COOH + NaOH —> CH3COO-Na+ + H2O)

Question 8

Carboxylic acid + Carbonate —>

Answer 8

-Salt + Water + Carbon dioxide
-Example- (CH3COOH + 1/2Na2CO3 –> CH3COO-Na+ +1/2H2O + 1/2CO2)

Question 9

Oxidation of methanoic acid

Answer 9

-Carboxylic acids can’t be oxidised by oxidising agents but methanoic acid is an exception as its structure has an aldehyde group.
-H-COOH + [O] —> HOCOOH
-Forms carbonic acid (H2CO3) which can decompose to give CO2.

Question 10

Esterification

Answer 10

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

Question 11

Use of esters

Answer 11

-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.
-Esters can be used as plasticisers for polymers.