OCR A Jun 2011 Paper 1 Q3

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The chlor-alkali industry is an important part of the UK chemical industry. The raw material is brine, a concentrated aqueous solution of sodium chloride, NaCl(aq). Two products that can be manufactured from brine are chlorine and sodium hydroxidehence the name chlor-alkali. (a) Bleach can be made by reacting chlorine with cold aqueous sodium hydroxide. A solution of bleach contains the chlorate compound NaClO. Write the equation for the reaction taking place.[1] (b) The systematic name for NaClO is sodium chlorate(I). Other chlorate compounds exist, such as NaClO3. (i) Give the systematic name for NaClO3.[1] (ii) When heated, NaClO3 disproportionates as shown in the equation below. 4NaClO3 3NaClO4 + NaCl Using oxidation numbers, explain why this is a disproportionation reaction.[3]OCR 2011<br />
 (c) Chlorine has been added to drinking water for over a century. Recently, some scientists have put forward the case for not chlorinating drinking water. This is because chlorine may react with organic compounds in the water to form CH3Cl. (i) State one valid reason that supports the scientists case and state one reason why chlorine should be added to drinking water.[2] (ii) Draw a dot-and-cross diagram to show the bonding in a molecule of CH3Cl. Show outer electrons only. [1] (iii) Name the shape of a molecule of CH3Cl .[1] (d) A sample of brine is a concentrated aqueous solution of sodium chloride, NaCl(aq). Describe a simple chemical test that you could carry out to show that brine contains aqueous chloride ions. How would you confirm that no other halide ions are present? Include an ionic equation in your answer.[4]OCR 2011 [Total: 13] Turn over<br />

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