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Report of redox titration— Iodine titrated against sodium thiosulphate Objectives The objective of this experiment is to balance the equation for the reaction between sodium thiosulphate and iodine. Principle As the reaction between sodium thiosulphate and iodine is a redox reaction, so I make use of this to perform a redox titration, iodine titrated against sodium thiosulphate.
From the experimental result, I can find out the number of mole of the two substances, hence I can calculate the mole ratio of the two substances. After find out the mole ratio, I can balance the equation of the reaction. And the indicator use in this experiment is starch solution, which is dark blue in colour in the presence of iodine. The disappearance of the dark blue colour is the end point of the titration. Results |Weight of Na2S2O3 |3. 0g | | |Trial |1 |2 |3 | |Final b r | | | | | |I reading | | | | | |Volume used/ | | | | | |Mean vol. | | | | Calculation 1. 2. Discussion From the results, the ratio of Na to Iodine is 2:1, and the balanced equation is _____. Iodine is the limiting agent; all the Iodine has form sodium iodide and the remaining Na has form ______. As iodine will react with starch solution to form a dark blue colour, so I use sodium thiosulphate titrate iodine, which have a sharply change to indicator the end point.
But if the starch solution added to soon, the compound formed from iodine and starch will have a compress because of stable, and I mat get a dark blue precipitate which dose not dissolve again even there is an excess of thiosulphate. The indicator will added when the solution is straw-coloured as it is indicate the iodine has almost gone. The experimental result is inaccurate because of three errors. Firstly, there may have lost of sodium thiosulphate during standardization.
Secondly, as iodine is a volatile gas, during the titration, the iodine may evaporate, which make the result inaccurate. Thirdly is the reaction time error made by me, I cannot stop the transfer of Sodium thiosulphate immediately when the titration is just finish. The safety precaution of this experiment is handle iodine carefully; do not let the iodine exposed in air, because iodine is toxic. If we inhale too much, we will feel sick. Conclusion To sum up, I can balance the equation accurately for the reaction between sodium thiosulphate and iodine by the redox titration.