OCR A Jan 2009 Paper 1 Q5

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The Group 2 element barium, Ba, is silvery white when pure but blackens when exposed to air. The blackening is due to the formation of both barium oxide and barium nitride. The nitride ion is N3. 11 (a) Predict the formula of: barium oxidebarium nitride[2] (b) A 0.11 g sample of pure barium was added to 100 cm3 of water. Ba(s) + 2H2O(l) Ba(OH)2(aq) + H2(g) (i) Show that 8.0104 mol of Ba were added to the water. (ii) Calculate the volume of hydrogen, in cm3, produced at room temperature and pressure. [1] (iii) Calculate the concentration, in mol dm3, of the Ba(OH)2(aq) solution formed. volume =cm3 [1] concentration =mol dm3 [1] (iv) State the approximate pH of the Ba(OH)2(aq) solution.[1] TURN OVER FOR QUESTION 5(c) AND 5(d)OCR 2009 Turn over<br />
 12 (c) A student repeated the experiment in (b) using a 0.11 g sample of barium that had blackened following exposure to the air. Suggest why the volume of hydrogen produced would be slightly less than the volume collected using pure barium.[1] (d) Describe and explain the trend, down the group, in the reactivity of the Group 2 elements with water.[5] [Total: 12] END OF QUESTION PAPER Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (OCR) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. OCR is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.OCR 2009<br />

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