OCR A Jun 2011 Paper 5 Q6

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16 6 Nickel is a typical transition element in the d-block of the Periodic Table. Many nickel ions are able to interact with ligands to form complex ions, such as [Ni(H2O)6]2+. (a) Using the information about nickel above, explain the meaning of the terms d-block element, transition element, ligand and complex ion. Include electron structures and diagrams in your answer.[7]OCR 2011<br /> (b) A student dissolves nickel(II) sulfate in water. A green solution forms containing the complex ion [Ni(H2O)6]2+. 17 The student then reacts separate portions of the green solution of nickel(II) sulfate as outlined below. Concentrated hydrochloric acid is added to the green solution of nickel(II) sulfate until there is no further change. The solution turns a lime-green colour and contains the four- coordinate complex ion A. Aqueous sodium hydroxide is added to the green solution of nickel(II) sulfate. A pale- green precipitate B forms. Concentrated aqueous ammonia is added to the green solution of nickel(II) sulfate until there is no further change. The solution turns a violet colour and contains the complex ion C. C has a molar mass of 160.7 g mol1. (i) Draw a 3-D diagram for the [Ni(H2O)6]2+ ion. Show a value for the bond angles on your diagram. (ii) Suggest the formulae of A and B. AB[2] (iii) Deduce the formula of C. [2] C[1] (iv) Write an equation for the formation of C from [Ni(H2O)6]2+.[2]OCR 2011 Turn over<br /> (c) 2,2'-Bipyridine (or bipy) is a bidentate ligand that forms complexes with many transition metals. The structure of 2,2'-bipyridine is shown below. 18 1' 2 N 2' 2,2'-bipyridine In the naming of bipyridines, the numbering starts at the carbon atom that links to the other ring. 2,2'-Bipyridine forms a complex, [Ni(bipy)2]2+. The structure of [Ni(bipy)2]2+ is shown in Fig 6.1 below. Ni2+ Ni2+ structure simplified diagram [Ni(bipy)2]2+ Fig 6.1 (i) What is the molecular formula of 2,2'-bipyridine?[1] (ii) What is the coordination number of the [Ni(bipy)2]2+ complex ion?[1]OCR 2011<br /> 19 (iii) 2,2'-Bipyridine forms a complex with the transition metal ruthenium with the formula [Ru(bipy)3]2+. This complex exists as two stereoisomers. Draw 3-D diagrams to predict the structures for these stereoisomers of [Ru(bipy)3]2+. You can represent the 2,2'-bipyridine ligands as in the simplified diagram for [Ni(bipy)2]2+ in Fig 6.1. (iv) 4,4'-Bipyridine (4,4'-bipy) can also form complexes with transition metal ions. Because of its structure, 4,4'-bipyridine can bridge between metal ions to form coordination polymers. For example, nickel(II) can form a coordination polymer with 4,4'-bipyridine containing {[Ni(H2O)4(4,4'-bipy)]2+}n chains. Draw a 3-D diagram to predict the repeat unit in this coordination polymer of nickel(II). Your diagram should show the complete structure of 4,4'-bipyridine and all coordinate bonds. [2] [3] [Total: 21] Turn overOCR 2011<br />

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