Edexcel Jun 2016 Paper 5 Q20

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SECTION B Answer ALL the questions. Write your answers in the spaces provided. 20 Vanadium exists in different oxidation states which can be interconverted using suitable oxidising and reducing agents. (a) Use relevant standard electrode potential values, on page 14 of the Data Booklet, to complete the table below in which two E (cid:57) values are missing. (1) Half-equation E (cid:57) / V V2+(aq) + 2e (cid:85) V(s) V3+(aq) + e (cid:85) V2+(aq) VO2+(aq) + 2H+(aq) + e (cid:85) V3+(aq) + H2O(l) I2(aq) + 2e (cid:85) 2I(aq) VO2 +(aq) + 2H+(aq) + e (cid:85) VO2+(aq) + H2O(l) +0.34 +0.54 +1.00 14 *P46661A01432* 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 A E R A S I H T N I E T I R W T O N O D (b) The standard electrode potential of V3+(aq) + e (cid:85) V2+(aq) is measured using the apparatus below. hydrogen gas platinum electrode solution containing H+(aq) (i) Identify, by name or formula, the substances needed in the salt bridge and the right-hand half-cell to measure the standard electrode potential. (3) A Salt bridge containing a solution ofB Electrode made ofC Solution containing(ii) State the three standard conditions needed for this measurement. (2) 123A E R A S I H T N I E T I R W T O N O D *P46661A01532* 15 Turn over<br /> *(c) A solution containing iodide ions, I, was added to an acidified solution +. containing vanadium(V) ions, VO2 Predict the oxidation state of the vanadium ions left at the end of the reaction. Justify your prediction by calculating the E(cid:57) cell for any relevant reaction(s). Write the ionic equation for any reaction(s) occurring. State symbols are not required. (5)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(Total for Question 20 = 11 marks) 16 *P46661A01632* 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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