OCR A Jun 2014 Paper 5 Q5

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5 Elements in the d-block of the Periodic Table form ions that combine with ligands to form complex ions. Most d-block elements are also classified as transition elements. 10 (a) Explain why two of the Period 4 d-block elements (ScZn) are not also transition elements. In your answer you should link full electron configurations to your explanations.[6] (b) The cobalt(III) ion, Co3+, forms a complex ion A with two chloride ligands and two ethanediamine, H2NCH2CH2NH2, ligands. The structure of ethanediamine is shown below. H2N NH2 (i) Explain how ethanediamine is able to act as a bidentate ligand.[2] (ii) Write the formula of complex ion A.[1] (iii) What is the coordination number of cobalt in complex ion A?[1]OCR 2014<br />
 (iv) Complex ion A has cis and trans stereoisomers. One of these stereoisomers also has an optical isomer. Draw 3-D diagrams to show the three stereoisomers. 11 Question 5 continues on page 12 [3]OCR 2014 Turn over<br />
 (c) The equilibrium reaction for the transport of oxygen by haemoglobin (Hb) in blood can be represented as equation 5.1. 12 Hb(aq) + O2(aq) HbO2(aq) equation 5.1 (i) Explain how ligand substitution reactions allow haemoglobin to transport oxygen in blood.[2] (ii) Write an expression for the stability constant, Kstab, for the equilibrium involved in the transport of oxygen by haemoglobin. Use the simplified species in equation 5.1. [1] (iii) In the presence of carbon monoxide, less oxygen is transported in the blood. Suggest why, in terms of bond strength and stability constants.[2] [Total: 18]OCR 2014<br />

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