Exam questions paper 1

Question 1

Describe what is seen when chlorine is added to a solution of bromide ions

Answer 1

an orange/brown solution forms

Question 2

DyeC has an orange colour.
(i) Explain why dyeC absorbs visible light.

Answer 2

electrons in the extended delocalised system absorb specific frequencies of visible light
electrons are raised to higher energy levels
frequency absorbed depends on energy gap as E=HV

Question 3

Comment on the solubility of the two dyes in water.
In your answer consider intermolecular bonds and their relative strengths.
Dye c= OH and N=N
Dye D= SO3- OH and N=N

Answer 3

solubility of dye c
forms fewer hydrogen bonds
Only form between O of phenol/-OH group and water and N of N=N group and water
Id-Id imbs form between rest of molecule and water
solubility of dye D
forms more hydrogen bonds than dye c
forms ion dipole bonds between SO3- groups and water

Question 4

Suggest a reagent and the conditions that would turn dyeC into dyeD (sulphonation)

Answer 4

Concentrated H2SO4
AND reflux

Question 5

Give the equations for the formation of a diazonium compound-reagants and conditions?

Answer 5

Reagants
NaNO2, HCl, aromatic amine
less than 5 degrees C
NaNO2 + HCl -> NaCl + HNO2
HNO2 + aromatic amine +HCl -> diazonium compound (triple bond N-N, positive charge on N attached to benzene ring)