OCR A Jan 2010 Paper 1 Q4

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4 Chlorine and bromine are elements in Group 7 of the Periodic Table. (a) Chlorine is used in water treatment. State one advantage and one disadvantage of using chlorine in water treatment. advantage:disadvantage:[2] (b) The electron configuration of bromine contains outermost electrons in the 4th shell. Using your knowledge of Group 7 elements, complete the electron configuration of bromine. 1s22s22p63s23p6[1] (c) Displacement reactions can be used to detect bromide ions in solution. A student has a solution that contains bromide ions. The student carries out the following experiment. Step 1 Step 2 She bubbles some chlorine gas through a sample of the solution. The mixture changes colour. The student then adds an organic solvent, cyclohexane, to the mixture. She shakes the contents and allows the layers to separate. (i) Write the ionic equation for the reaction that takes place in step 1.[1] (ii) What colour does the cyclohexane layer turn in step 2?[1]OCR 2010<br /> (d) Chlorine reacts differently with dilute and concentrated aqueous solutions of sodium hydroxide. When chlorine reacts with dilute sodium hydroxide, one of the products is sodium chlorate(I). This is the reaction that is used to manufacture bleach. When chlorine is reacted with hot concentrated sodium hydroxide, a different reaction takes place. One of the products is NaCl O3, used as a weedkiller. In each reaction, chlorine has been both oxidised and reduced. (i) What term is used to describe a redox reaction in which an element is both oxidised and reduced?[1] (ii) Write equations for these two reactions of chlorine with sodium hydroxide: equation for reaction with dilute sodium hydroxide,equation for reaction with hot concentrated sodium hydroxide.[3] (iii) Chlorine forms another chlorate called sodium chlorate(VII), used in the manufacture of matches. Suggest the formula of sodium chlorate(VII).[1] [Total: 10]OCR 2010 Turn over<br />

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