OCR A Jun 2010 Paper 1 Q4

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In the Periodic Table, the chemistry of elements in a group can often be predicted from the chemistry of just one element in the group. (a) Ions of Group 7 elements take part in displacement reactions. These reactions can be used to compare the reactivities of the elements within Group 7. A student adds aqueous solutions of halogens to test-tubes containing solutions of halide ions. The resulting mixtures are then shaken with cyclohexane, an organic solvent. One of the students results is shown in the table. experiment number experiment details colour seen within the organic solvent addition of Cl 2(aq) to I (aq) ions addition of Cl 2(aq) to Br (aq) ions addition of Br2(aq) to Cl (aq) ions orange (i) Complete the table to show the expected colours. [2] (ii) Write the ionic equation for the reaction taking place in experiment 2.[1] (iii) These three experiments alone are unable to confirm the order of reactivity for Cl 2, Br2 and I2. Suggest one further displacement reaction which could be carried out to confirm the order of reactivity of Cl 2, Br2 and I2.[1] (b) Chlorine gas reacts with water as shown below. Cl 2(g) + H2O(l) HCl O(aq) + HCl (aq) (i) Using oxidation numbers, explain why this reaction is an example of disproportionation.[3]OCR 2010<br />
 (ii) State one benefit for public health, of the reaction between chlorine gas and water.[1] (c) Group 2 elements and compounds show periodic trends. One trend is shown by the effect of heat upon Group 2 carbonates. A student carried out an experiment to find out the volume of carbon dioxide obtained by heating a weighed sample of magnesium carbonate. The student placed a 1.47 g sample of MgCO3 into a test-tube and heated it until there was no further change in mass. The following reaction took place. MgCO3(s) MgO(s) + CO2(g) (i) What type of reaction is this?[1] (ii) What volume of CO2, in dm3, would have been given off when measured at room temperature and pressure? The molar mass of MgCO3 = 84.3 g mol1 answer = dm3 [2] (iii) The student repeated the experiment a further three times, using the same number of moles of CaCO3, SrCO3 and BaCO3. What trend in the behaviour of the Group 2 carbonates would be observed by the student?[1]OCR 2010 [Total: 12] Turn over<br />

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