Edexcel Jun 2017 Paper 5 Q21

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21 This question is about the chemistry of chromium. (a) The graph below shows the first and second ionization energies of the elements scandium to manganese. 15001300ionization energy / KJ mol1 1100Ti Sc Cr Second Mn 900700500Sc Ti Cr First Mn (i) Explain why the values for the first ionization energies are very similar. (2)14 *P48070A01428* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> A E R A S I H T N I E T I R W T O N O D *(ii) The electronic configuration of a chromium atom is [Ar] 3d54s1 By considering the electronic configurations of the singly charged ions of vanadium, chromium and manganese, suggest why the second ionization energy of chromium is higher than the corresponding values for vanadium and manganese. (3)A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P48070A01528* 15 Turn over<br /> (b) The table below shows the formulae of ions of chromium which exist in aqueous solution. Ion Oxidation number of chromium Colour in aqueous solution +2 Blue 2+ Cr(H2O)6 3+ Cr(H2O)6 2 CrO4 2 Cr2O7 D O N O T W R I T E I N T H I S A R E A (i) Complete the table above by adding the missing oxidation numbers and colours. (3) *(ii) Explain why the Cr(H2O)6 3+ ion is coloured. (4)16 *P48070A01628* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> (iii) A solution containing aqueous Cr3+ ions reacts with zinc in suitable conditions to form Cr2+ ions and Zn2+ ions. Draw a diagram of a cell that can be used to measure E cell for the reaction. State the conditions which are necessary. (iv) Use your Data booklet to calculate E cell. (3) (2) A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P48070A01728* 17 Turn over<br /> (c) A solution containing Cr3+(aq) ions is oxidized by hydrogen peroxide in the presence of hydroxide ions to form CrO4 2 ions. The half-equation for the reduction of hydrogen peroxide is H2O2(aq) + 2e (cid:111) 2OH(aq) (i) Write the half-equation for the oxidation of Cr3+(aq) in the presence of hydroxide ions to form CrO4 2ions. (ii) Hence write the overall equation for this reaction. (d) Write the equation for the reaction of chromate(VI) ions with hydrogen ions. D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A (1) (1) (1) (Total for Question 21 = 20 marks) 18 *P48070A01828* D O N O T W R I T E I N T H I S A R E A<br />

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