OCR A Jan 2013 Paper 1 Q5

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5 Hydrogen chloride is a colourless gas which forms white fumes in moist air. 10 (a) Molecules of hydrogen chloride, HCl, and molecules of fluorine, F2, contain the same number of electrons. Hydrogen chloride boils at 85 C and fluorine boils at 188 C. Explain why there is a difference in the boiling points of HCl and F2. In your answer you should refer to the types of force acting between molecules and the relative strength of the forces between the molecules. In your answer, you should use appropriate technical terms, spelled correctly.[4] (b) Hydrogen chloride reacts with water to produce an ion with the formula H3O+. An H3O+ ion has one dative covalent bond. Draw a dot-and-cross diagram to show the bonding in H3O+. Show outer electrons only.OCR 2013 [2]<br />
 11 (c) Borax, Na2B4O710H2O, can be used to determine the concentration of acids such as dilute hydrochloric acid. A student prepares 250 cm3 of a 0.0800 mol dm3 solution of borax in water in a volumetric flask. Calculate the mass of borax crystals, Na2B4O710H2O, needed to make up 250 cm3 of 0.0800 mol dm3 solution. answer =g [3] Question 5 continues on page 12OCR 2013 Turn over<br />
 (d) The student found that 22.50 cm3 of 0.0800 mol dm3 Na2B4O7 reacted with 25.00 cm3 of dilute hydrochloric acid. 12 Na2B4O7 + 2HCl + 5H2O 2NaCl + 4H3BO3 (i) Calculate the amount, in mol, of Na2B4O7 used. (ii) Calculate the amount, in mol, of HCl used. amount =mol [1] (iii) Calculate the concentration, in mol dm3, of the HCl. amount =mol [1] concentration =mol dm3 [1] [Total: 12] 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 2013<br />

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