Edexcel Jan 2014 (IAL) Paper 2 Q21

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SECTION B Answer ALL the questions. Write your answers in the spaces provided. 21 Iodine pentoxide, I2O5, is a white crystalline solid. It is formed by heating HIO3 to about 200 C in a stream of dry air. The reaction is shown below. 2HIO3 (cid:85) I2O5 + H2O (a) (i) Is this production of iodine pentoxide a redox reaction? Justify your answer by stating the oxidation number of iodine in both of these compounds. (1)(ii) Suggest why it is important to have a stream of dry air. (1)(iii) Above 300 C, iodine pentoxide decomposes to form iodine and oxygen. Write the equation for this decomposition. State symbols are not required. (1) *P42987A0820*<br /> (iv) In iodine pentoxide, each iodine atom is bonded to three oxygen atoms and one of these oxygen atoms is bonded to both iodine atoms as shown in the layout below. Complete the dot and cross diagram for the molecule, using dots for the oxygen electrons and crosses for the iodine electrons. In this molecule, each iodine atom has twelve electrons in its outer shell. Show outer shell electrons only. (v) The shape around the iodine is similar to that around the nitrogen in ammonia, NH3. Suggest a value for the OIO bond angle and the name of the shape around the iodine atom. (2) (2) OIO bond angleShape*P42987A0920* Turn over<br /> (b) Iodine pentoxide is used as a reagent to determine the amount of carbon monoxide present in a gaseous sample. The sample is passed over heated iodine pentoxide. The products of this process are carbon dioxide and iodine. The iodine formed is extracted and added to an excess of sodium thiosulfate solution of known concentration. The remaining sodium thiosulfate is then determined by titration with a solution of iodine of known concentration. I2(aq) + 2S2O3 2(aq) (cid:111) 2I(aq) + S4O6 2(aq) In an analysis, a 2.00 m3 sample of gas was used and the resultant iodine extracted and added to 20 cm3 of a 0.0400 mol dm3 solution of sodium thiosulfate, an excess. The resultant solution was then titrated against a solution of iodine of concentration 0.0100 mol dm3. The volume of iodine solution required for complete reaction was 21.60 cm3. (i) Calculate the number of moles of iodine present in 21.60 cm3 of the iodine solution. Give your answer to three significant figures. (ii) Deduce the number of moles of sodium thiosulfate that reacted with this titrated amount of iodine. (iii) Calculate the number of moles of sodium thiosulfate to which the iodine was initially added. (iv) From your answers to parts (b)(ii) and (b)(iii), determine the number of moles of sodium thiosulfate that reacted with the extracted iodine. (v) Use your answer to part (b)(iv) to determine the number of moles of extracted iodine. (1) (1) (1) (1) (1) 10 *P42987A01020*<br /> (vi) Write the balanced equation for the reaction between iodine pentoxide and carbon monoxide. State symbols are not required. (vii) Calculate the volume, in dm3, of carbon monoxide in the original gaseous sample. Assume that the molar gas volume of any gas under the experimental conditions is 24 dm3 mol1. (viii) State how this procedure could be amended to produce results that are more reliable. (1) (2) (1)*(c) Carbon monoxide is an atmospheric pollutant arising from the incomplete combustion of fossil fuels. (i) State how motor vehicles have been adapted to reduce the production of this pollutant. (1)(ii) Explain the meaning of the term carbon-neutral and give an example of a motor vehicle fuel that can be classified in this way. (2)(Total for Question 21 = 19 marks) *P42987A01120* 11 Turn over<br />

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