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UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level

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CHEMISTRY Advanced Practical Skills 2

9701/32 May/June 2012 2 hours

Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions

READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Give details of the practical session and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. You may lose marks if you do not show your working or if you do not use appropriate units. Use of a Data Booklet is unnecessary. Qualitative Analysis Notes are printed on pages 11 and 12. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Session


For Examiner’s Use 1 2 Total This document consists of 12 printed pages.
IB12 06_9701_32/5RP © UCLES 2012

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2 1 Iodide ions are oxidised by iron(III) ions in the presence of acid. 2Fe3+(aq) + 2I–(aq) → 2Fe2+(aq) + I2(aq) The rate of this reaction can be measured by adding thiosulfate ions, S2O32–, and some starch indicator to the mixture. As the iodine is produced, it reacts immediately with the thiosulfate ions and is reduced back to iodide ions. I2(aq) + 2S2O32–(aq) → 2I–(aq) + S4O62–(aq) When all the thiosulfate ions have reacted, the iodine which continues to be produced then turns the starch indicator blue-black. The rate of reaction may be determined by timing how long it takes for the reaction mixture to turn blue-black. You are to investigate how the rate of reaction is affected by changing...


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