Edexcel Jan 2010 Paper 2 Q17

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PMT 17 This question is about some reactions of halogens and halide ions. (a) (i) When chlorine is added to a solution containing bromide or iodide ions, a colour change occurs. What solvent would you add to the mixture to confirm the identity of the halogen produced? (1)(ii) Give the result for the test with this solvent in a reaction in which bromine is produced. (1)(b) (i) Solid potassium bromide and potassium iodide can be distinguished by their reactions with concentrated sulfuric acid. Potassium bromide reacts with concentrated sulfuric acid initially to produce hydrogen bromide. This reacts further, as shown below, to produce a sharp smelling gas and a brown fuming liquid. 2HBr(g) + H2SO4(l)SO2(g) + Br2(l) + 2H2O(l) Show, by use of oxidation numbers for sulfur, that the sulfuric acid has been reduced. (2)(ii) State TWO observations, which would differ from those with potassium bromide, when potassium iodide reacts with concentrated sulfuric acid. (2)12 *N35692A01224*<br /> PMT (iii) One product of the reaction with potassium iodide is hydrogen sulfide, H2S. How does this show that iodide ions are more powerful reducing agents than bromide ions? (1)(c) In areas where the natural concentration of fluoride ions in rocks is low, some water authorities add fluoride to the water supply to improve the dental health of children. An alternative would be to supply free fluoride tablets. Give ONE reason why it could be considered more ethical to supply free fluoride tablets rather than to add fluoride compounds to the water supply. (1)(Total for Question 17 = 8 marks) *N35692A01324* 13 Turn over<br />

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