AQA Jun 2013 Paper 5 Q8

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do not write outside the box this question explores some reactions and some uses of cobalt compounds a ethanal is oxidised to ethanoic acid by oxygen the equation for this reaction is ch cho o ch cooh this redox reaction is slow at room temperature but speeds up in the presence of cobalt compounds explain why a cobalt compound is able to act as a catalyst for this process illustrate your explanation with two equations to suggest how in the presence of water and hydrogen ions co and then co ions could be involved in catalysing this reaction marks wmp jun chem do not write outside the box b in aqueous solution the co h o ion reacts with an excess of ethane diamine to form the complex ion y b i write an equation for this reaction explain in terms of the chelate effect why the complex ion y is formed in preference to the co h o complex ion marks b ii draw a diagram that shows the shape of the complex ion y and shows the type of bond between the ethane diamine molecules and the cobalt question continues on the next page marks turn over wmp jun chem do not write outside the box c compound z is a complex that contains only cobalt nitrogen hydrogen and chlorine a solid sample of z was prepared by reaction of cm of mol dm aqueous cobalt ii chloride with ammonia and an oxidising agent followed by hydrochloric acid when this sample of z was reacted with an excess of silver nitrate g of silver chloride were obtained use this information to calculate the mole ratio of chloride ions to cobalt ions in z give the formula of the complex cobalt compound z that you would expect to be formed in the preparation described above suggest one reason why the mole ratio of chloride ions to cobalt ions that you have calculated is different from the expected value marks end of questions copyright aqa and its licensors all rights reserved wmp jun chem

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