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Oxford Cambridge and RSA
RES45ER6 76RE5DFVB 6F5 76765 43ERDFGH UYT56TYUOHGCEX3WECVB YTTYUKERDT TFYU87T TUUGYYYYYY
HFGCT GY T GYGVH HYFUCG Y6888888888TC Y67TG GR7YVG T7UGHRF7 76FTGH
A-Level OCR 2025 Chemistry B (Salters) Paper 2
Monday 16 June 2025 – Morning
A Level Chemistry B (Salters)
H433/02 Scientific literacy in chemistry
Time allowed: 2 hours 15 minutes
1
Turn over
, 2
1 This question is about reactions of haloalkanes.
(a) CH3Cl is made by plants that grow on marshes.
If CH3Cl reaches the stratosphere, electromagnetic radiation causes it to undergo homolytic
fission forming chlorine radicals.
(i) Give the systematic name of CH3Cl .
...................................................................................................................................................................... [1]
(ii) Draw ‘half curly arrows’ to show the mechanism of the homolytic fission of CH3Cl .
Show the products of the reaction.
H
H C Cl
H
[2]
(iii) Which type of electromagnetic radiation causes this homolytic fission to occur in the stratosphere?
...................................................................................................................................................................... [1]
(iv) The bond energy of the C–Cl bond is 346 kJ mol–1.
Calculate the wavelength (in m) of radiation which breaks this bond.
Give your answer to an appropriate number of significant figures.
Wavelength = ..................................................... m [5]
(v) Chlorine radicals catalyse the breakdown of ozone in the stratosphere.
Write equations to show how this occurs and give the overall equation.
Overall equation:
[2]
© OCR 2025
, 3
(vi) Why is the breakdown of ozone in the stratosphere harmful to humans?
..........................................................................................................................................................
..........................................................................................................................................................
...................................................................................................................................................................... [2]
(b) CH3Cl reacts with ammonia to give an amine salt.
CH3Cl + NH3 CH3NH3Cl Equation 1.1
Ammonia is acting as a nucleophile here.
(i) Explain what is meant by the term nucleophile.
..........................................................................................................................................................
...................................................................................................................................................................... [1]
(ii) Show the mechanism of Equation 1.1.
Use curly arrows and show relevant lone pairs and the ionic products.
H
H C Cl
H
H N H
H
[2]
(iii) The product of Equation 1.1 is a salt of CH3NH2.
Give the systematic name for CH3NH2.
...................................................................................................................................................................... [1]
(c) The reaction between a haloalkane and hydroxide ions is a nucleophilic substitution reaction.
A student reacts 1-chlorobutane, 1-bromobutane and 1-iodobutane separately with aqueous
sodium hydroxide.
Which will react fastest and why?
..........................................................................................................................................................
..........................................................................................................................................................
...................................................................................................................................................................... [2]
© OCR 2025 Turn over
Oxford Cambridge and RSA
RES45ER6 76RE5DFVB 6F5 76765 43ERDFGH UYT56TYUOHGCEX3WECVB YTTYUKERDT TFYU87T TUUGYYYYYY
HFGCT GY T GYGVH HYFUCG Y6888888888TC Y67TG GR7YVG T7UGHRF7 76FTGH
A-Level OCR 2025 Chemistry B (Salters) Paper 2
Monday 16 June 2025 – Morning
A Level Chemistry B (Salters)
H433/02 Scientific literacy in chemistry
Time allowed: 2 hours 15 minutes
1
Turn over
, 2
1 This question is about reactions of haloalkanes.
(a) CH3Cl is made by plants that grow on marshes.
If CH3Cl reaches the stratosphere, electromagnetic radiation causes it to undergo homolytic
fission forming chlorine radicals.
(i) Give the systematic name of CH3Cl .
...................................................................................................................................................................... [1]
(ii) Draw ‘half curly arrows’ to show the mechanism of the homolytic fission of CH3Cl .
Show the products of the reaction.
H
H C Cl
H
[2]
(iii) Which type of electromagnetic radiation causes this homolytic fission to occur in the stratosphere?
...................................................................................................................................................................... [1]
(iv) The bond energy of the C–Cl bond is 346 kJ mol–1.
Calculate the wavelength (in m) of radiation which breaks this bond.
Give your answer to an appropriate number of significant figures.
Wavelength = ..................................................... m [5]
(v) Chlorine radicals catalyse the breakdown of ozone in the stratosphere.
Write equations to show how this occurs and give the overall equation.
Overall equation:
[2]
© OCR 2025
, 3
(vi) Why is the breakdown of ozone in the stratosphere harmful to humans?
..........................................................................................................................................................
..........................................................................................................................................................
...................................................................................................................................................................... [2]
(b) CH3Cl reacts with ammonia to give an amine salt.
CH3Cl + NH3 CH3NH3Cl Equation 1.1
Ammonia is acting as a nucleophile here.
(i) Explain what is meant by the term nucleophile.
..........................................................................................................................................................
...................................................................................................................................................................... [1]
(ii) Show the mechanism of Equation 1.1.
Use curly arrows and show relevant lone pairs and the ionic products.
H
H C Cl
H
H N H
H
[2]
(iii) The product of Equation 1.1 is a salt of CH3NH2.
Give the systematic name for CH3NH2.
...................................................................................................................................................................... [1]
(c) The reaction between a haloalkane and hydroxide ions is a nucleophilic substitution reaction.
A student reacts 1-chlorobutane, 1-bromobutane and 1-iodobutane separately with aqueous
sodium hydroxide.
Which will react fastest and why?
..........................................................................................................................................................
..........................................................................................................................................................
...................................................................................................................................................................... [2]
© OCR 2025 Turn over
