Edexcel Jan 2016 (IAL) Paper 2 Q24

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SECTION C Answer ALL the questions. Write your answers in the spaces provided. 24 This question is about some aspects of the chemistry of iodine and its compounds. In industry, the main source of iodine is sodium iodate(V), NaIO3, which occurs in deposits found in Chile. In the human body, iodide ions, I, are needed for the thyroid gland to function properly. In many countries, potassium iodide, KI, is added to table salt as a source of iodide ions. (a) In the production of iodine, the final stage involves the reaction between sodium iodate(V) and sodium iodide in acidic solution. The ionic half-equations for the redox processes are as follows.+ 6H+ + 5e (cid:111) I2 + 3H2O (cid:111) I2 + e IO3 I 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 A E R A S I H T N I E T I R W T O N O D (i) Use these half-equations to deduce the full ionic equation for the production of iodine by this process. State symbols are not required. (ii) Identify, by its formula, the oxidizing agent in the reaction in (a)(i). Justify your answer in terms of electron transfer. (2) (1) I E T I R W T O N O D*P46938A01924* 19 Turn over<br /> (b) On addition of concentrated sulfuric acid to crystals of potassium iodide, solid sulfur and a black solid are observed amongst the products formed. (i) Identify, by name or formula, the black solid. (1)(ii) Construct the ionic half-equation for the formation of sulfur from concentrated sulfuric acid. State symbols are not required. (iii) When iodide ions react with concentrated sulfuric acid, another product, X, can also be detected. X is a toxic gas with a smell of rotten eggs. Identify X, by name or formula, and give the oxidation numbers of sulfur when X is formed from concentrated sulfuric acid. (2) (3) Identity of gas X: Oxidation number of S in sulfuric acid isOxidation number of S in X is20 *P46938A02024* 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 /> (c) The Recommended Dietary Allowance, RDA, of iodide ions in a balanced diet is 140 (cid:541)g per day. (1 (cid:541)g = 1106 g). (i) Calculate the mass, in (cid:541)g, of potassium iodide, KI, needed to supply the RDA of iodide ions. Give your answer to three significant figures. (2) Mass of KI =(cid:541)g (ii) Suggest a reason, other than cost, why some countries do not add potassium iodide to table salt. (1)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 *P46938A02124* 21 Turn over<br /> (d) (i) When chlorine is passed over iodine crystals, iodine monochloride, ICl, is formed. Iodine monochloride, ICl, is a liquid at room temperature whereas chlorine, Cl2, is a gas. Explain, in terms of intermolecular forces, why this is so. (4)(ii) When excess chlorine is passed over iodine monochloride, iodine trichloride, ICl3, is formed. Draw the dot and cross diagram of ICl3, showing only the outer electrons. (2) 22 *P46938A02224* 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 (e) When chlorine gas is bubbled into aqueous potassium iodide solution, a redox reaction occurs. (i) Give the ionic equation for this reaction. State symbols are not required. (ii) In a further experiment, 0.50 mol of chlorine gas was bubbled into an aqueous solution containing a mixture of 0.66 mol of sodium iodide and 0.66 mol of sodium bromide. Assuming that all the chlorine gas reacted, calculate the number of moles of iodine and bromine produced. Justify your answer in terms of the relative reducing power of bromide and iodide ions. (1) (3) The number of moles of iodine produced: A E R A S I H T N The number of moles of bromine produced: I E T I R W T O N O D JustificationA E R A S I H T N I E T I R W T O N O D(Total for Question 24 = 22 marks) TOTAL FOR SECTION C = 22 MARKS TOTAL FOR PAPER = 80 MARKS *P46938A02324* 23<br />

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