Edexcel Jun 2014 (R) Paper 1 Q22

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22 When trichloromethane, CHCl3, reacts with chlorine, the organic product is tetrachloromethane, CCl4. The reaction proceeds by free radical substitution. The equation for this reaction is CHCl3 + Cl2 (cid:111) CCl4 + HCl (a) State the essential condition for this reaction to occur at room temperature. (1)(b) The reaction mechanism involves free radicals. Explain what is meant by the term free radical. (1)(c) The reaction takes place in a series of steps. (i) The initiation step is Cl2 (cid:111) 2Cl Suggest why this initiation step is more likely than CHCl3 (cid:111) CCl3 + H (1)(ii) Write equations for the two propagation steps. (2) First propagation step Second propagation step 22 *P42990A02228*<br /> (iii) Write an equation for the termination step in which tetrachloromethane is formed. (d) Tetrachloromethane can be manufactured using the by-products of chlorination reactions. C2Cl6 + Cl2 (cid:111) 2CCl4 Compare the atom economy of this process with that of the reaction which produces tetrachloromethane from trichloromethane and chlorine. A calculation is not required. (1) (1)(Total for Question 22 = 7 marks) *P42990A02328* 23 Turn over<br /> BLANK PAGE 24 *P42990A02428*<br />

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