OCR A Jan 2011 Paper 1 Q4

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4 Calcium hydroxide is used in agriculture but the amounts used must be carefully controlled. (a) State one use of calcium hydroxide in agriculture and suggest why the amount of calcium hydroxide used should not be excessive.[2] (b) A student knew that calcium hydroxide could be made by adding calcium to water. The student added 0.00131 mol of calcium to a beaker containing about 100 cm3 of water. A reaction took place as shown by the equation below. All the calcium hydroxide formed was soluble. Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g) (i) Calculate the mass of calcium that the student added. mass of calcium =g [1] (ii) Calculate the volume of hydrogen gas, in dm3, produced in this reaction at room temperature and pressure, RTP. volume of hydrogen gas =dm3 [1] (iii) The student transferred the contents of the beaker to a 250 cm3 volumetric flask and water was added to make the solution up to 250 cm3. Calculate the concentration, in mol dm3, of hydroxide ions in the 250 cm3 solution.OCR 2011 concentration =mol dm3 [2]<br />
 (c) The student repeated the experiment using the same mass of pure barium. The student found that a smaller volume of hydrogen gas was produced, measured at RTP. (i) Explain why.[1] (ii) Suggest one other difference the student would observe between the reactions of water with calcium and of water with barium.[1] [Total: 8]OCR 2011 Turn over<br />

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