Edexcel Jun 2017 Paper 5 Q8

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6 Dilute aqueous sodium hydroxide and dilute aqueous ammonia are added to separate samples of aqueous nickel(II) chloride. In each case a green precipitate forms. What would be observed when excess alkali is added to the green precipitate? Addition of excess NaOH(aq) Addition of excess NH3(aq) A Precipitate remains Precipitate remains B Precipitate remains Precipitate dissolves to form a blue solution C Precipitate dissolves to form a green solution Precipitate remains D Precipitate dissolves to form a green solution Precipitate dissolves to form a blue solution In the reaction of sodium thiosulfate solution with iodine, the half-equation for the reaction of the thiosulfate ions is (Total for Question 6 = 1 mark) A S B S 2O3 2 + 3H2O (cid:111) 2SO3 2 + 6H+ + 4e 2O3 2 + 3H2O + 4e (cid:111) 2SO3 2 + 6H+ C 2S 2O3 2 + 2e (cid:111) S4O6 2 D 2S 2O3 2 (cid:111) S4O6 2 + 2e (Total for Question 7 = 1 mark) In the titration of sodium thiosulfate solution with iodine, starch indicator is added near the end-point. This is because there is no warning of the end-point if starch is added at the start. B high concentrations of iodine decompose the starch. the blue-black colour showing the presence of iodine would not be seen. D an insoluble complex forms between starch and high concentrations of iodine. Use this space for any rough working. Anything you write in this space will gain no credit. (Total for Question 8 = 1 mark) *P48070A0428* 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 />

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