OCR A Jun 2016 Paper 5 Q7

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7 Hydroxide ions, OH, and cyanide ions, CN, can react with some aqueous solutions of transition metal compounds. 16 (a) When nickel(II) sulfate is dissolved in water, a pale green solution forms containing a six-coordinate complex ion C. Aqueous potassium hydroxide is added to aqueous nickel(II) sulfate. A green solid D forms. An excess of aqueous potassium cyanide is added to aqueous nickel(II) sulfate. A yellow solution forms containing a four-coordinate complex ion E that contains only nickel, carbon and nitrogen. (i) In C, D and E, nickel has the +2 oxidation state. Suggest the formulae of C, D and E. Complex ion C:Solid D:Complex ion E:[3] (ii) Write equations, and name the types of reaction, for the formation of D and E. Formation of solid D from aqueous nickel(II) sulfate. Equation:Type of reaction:Formation of complex ion E from complex ion C. Equation:Type of reaction:[4]OCR 2016<br />
 (b) In some gold mines, cyanide is used to extract gold from its ore. 17 Gold metal in the ore reacts with cyanide ions, water and oxygen to form a water-soluble complex ion, [Au(CN)2], with a bond angle of 180. Hydroxide ions are also formed. (i) Name the shape of [Au(CN)2].[1] (ii) Using oxidation numbers, show that a redox reaction takes place.[2] (iii) Construct the overall equation for this reaction. State symbols are not required.[2] (iv) Some owners of gold mines remove cyanide ions from waste by adding oxidising agents, such as chlorate(I) ions, before discharge into watercourses. The overall equation is shown below. CN(aq) + ClO(aq) + 2H2O(l) NH4 +(aq) + CO3 2(aq) + Cl (aq) The oxidation half-equation is: CN + 3H2O + + CO3 NH4 2 + 2H+ + 2e Construct the reduction half-equation. State symbols are not required.[1]OCR 2016 [Total: 13] Turn over<br />

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