OCR A Jan 2012 Paper 1 Q5

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5 Ammonia, NH3, and hydrazine, N2H4, are both bases. 10 (a) Ammonium sulfate, (NH4)2SO4, can be prepared by reacting ammonia with sulfuric acid, H2SO4. (i) Why can ammonium sulfate be described as a salt?[1] (ii) A student was given 400 cm3 of aqueous ammonia solution, NH3(aq). The student was asked to determine how many moles of NH3 had been dissolved to prepare the solution. The student titrated 25.0 cm3 of NH3(aq) and found that it reacted exactly with 32.5 cm3 of 0.100 mol dm3 sulfuric acid. The equation for this reaction is shown below. 2NH3(aq) + H2SO4(aq) (NH4)2SO4(aq) Calculate the amount, in moles, of NH3 in the original 400 cm3 solution. answer =mol [3]OCR 2012<br />
 (b) The hydrazine molecule, H2NNH2, is covalent. 11 Predict the HNH bond angle in a hydrazine molecule. Explain your answer.[4] (c) Like ammonia, hydrazine is a base that reacts with water to form negative and positive ions. (i) Write the formula of the negative ion that is formed when hydrazine reacts with water.[1] (ii) Suggest the formula of a positive ion which might form when hydrazine reacts with water.[1] TURN OVER FOR QUESTION 5(d)OCR 2012 Turn over<br />
 (d) Hydrazine, N2H4, has found a use as rocket fuel. 12 The overall equation for the production of hydrazine is shown below. 2NH3 + NaCl O N2H4 + NaCl + H2O (i) Using oxidation numbers, explain why the above equation represents a redox reaction.[3] (ii) What is the name for NaCl O?[1] (iii) The overall reaction takes place in two stages.In the first stage NH2Cl is produced. In the second stage N2H4 is produced. Some of the hydrazine reacts with NH2Cl to form ammonium chloride and a colourless gas with a relative molecular mass of 28.0. Construct the equation for this reaction.[2] [Total: 16] END OF QUESTION PAPER Copyright Information OCR is committed to seeking permission to reproduce all third-party content that it uses in its assessment materials. OCR has attempted to identify and contact all copyright holders whose work is used in this paper. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced in the OCR Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download from our public website (www.ocr.org.uk) after the live examination series. If OCR has unwittingly failed to correctly acknowledge or clear any third-party content in this assessment material, OCR will be happy to correct its mistake at the earliest possible opportunity. For queries or further information please contact the Copyright Team, First Floor, 9 Hills Road, Cambridge CB2 1GE. 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 2012<br />

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