Modern Analytical Techniques I (Edexcel A Level Chemistry): Exam Questions

This question is about organic compounds containing fluorine and chlorine.

The use of chlorofluorocarbons as refrigerants has ceased due to concerns about their effects on the ozone layer. One such compound is dichlorodifluoromethane.

Give the molecular formula of dichlorodifluoromethane.

i) A different refrigerant contains 34.0% chlorine and 54.5% fluorine by mass, with the remainder carbon.

Calculate the empirical formula of this compound.

(3)

ii) Use the mass spectrum to show that the empirical and the molecular formulae of this compound are the same.

(1)

iii) Suggest the species responsible for the peak at m/z = 69.

(1)

Compounds containing carbon and fluorine but no chlorine can be used as refrigerants as they are not harmful to the ozone layer. These can be made by the reaction of fluorine with alkanes or fluoroalkanes. A refrigerant currently in use contains the compound trifluoromethane, CHF₃.

i) Write the equation for the formation of trifluoromethane by the reaction of difluoromethane with fluorine. State symbols are not required.

(1)

ii) The mechanism for this reaction is similar to that of the reaction between chlorine and methane.

Give the equations for the following steps in the mechanism for the reaction between fluorine and difluoromethane. Curly arrows are not required.

(3)

Initiation step

First propagation step

Second propagation step