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# An iodine / thiosulfate titration - Yola

An iodine / thiosulfate titration Specimen Results (standardising a thiosulfate solution). 3. Rough titre = cm Theory 3. Second titre = cm Aqueous iodine solutions normally contain potassium iodide (KI), 3. Third titre = cm which acts to keep the iodine in solution. This is due to the fact that an 3. Average of accurate titres = cm equilibrium is set up as follows: 3. Volume of iodine solution used in each titration = cm - - I2 + I I3 Concentration of iodine solution = M. - - I3 is much more soluble than I2 and it is as I3 the iodine is kept in solution. Specimen Calculations In this experiment, a standard ( M) solution of iodine is generated VA x MA x nB = VB x MB x nA. in the conical flask by reacting a standard ( M) solution of potassium iodate, for each titration , with excess potassium iodide. x MA x 1 = x x 2. iodine is liberated from iodate and iodide according to the equation: - - +.

An iodine / thiosulfate titration Theory Aqueous iodine solutions normally contain potassium iodide (KI), which acts to keep the iodine in solution.

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### Transcription of An iodine / thiosulfate titration - Yola

1 An iodine / thiosulfate titration Specimen Results (standardising a thiosulfate solution). 3. Rough titre = cm Theory 3. Second titre = cm Aqueous iodine solutions normally contain potassium iodide (KI), 3. Third titre = cm which acts to keep the iodine in solution. This is due to the fact that an 3. Average of accurate titres = cm equilibrium is set up as follows: 3. Volume of iodine solution used in each titration = cm - - I2 + I I3 Concentration of iodine solution = M. - - I3 is much more soluble than I2 and it is as I3 the iodine is kept in solution. Specimen Calculations In this experiment, a standard ( M) solution of iodine is generated VA x MA x nB = VB x MB x nA. in the conical flask by reacting a standard ( M) solution of potassium iodate, for each titration , with excess potassium iodide. x MA x 1 = x x 2. iodine is liberated from iodate and iodide according to the equation: - - +.

2 IO3 + 5I + 6H 3I2 + 3H2O. MA = x x 2 / ( x 1). The iodine solution, which is a golden-brown colour, can be titrated against sodium thiosulfate solution. The sodium thiosulfate solution is Concentration of sodium thiosulfate solution = M. placed in the burette and, as it is added to the conical flask, it reacts with the iodine and the colour of the solution fades. When it reaches a Specimen Results (standardising an iodine solution). pale yellow colour, a few drops of a freshly prepared starch solution 3. are added. The solution becomes blue-black, and the titration is Rough titre = cm 3. continued until it goes colourless. Second titre = cm 3. Third titre = cm 3. The titration reaction may be represented by the equation: Average of accurate titres = cm 2- - 2- 3. I2 + 2S2O3 2I + S4O6 Volume of iodine solution used in each titration = cm Concentration of sodium thiosulfate solution = M.

3 (Note that in this experiment a standard solution of iodine is used to standardise a sodium thiosulfate solution. But you also need to know Specimen Calculations that a standard solution of sodium thiosulfate can be used to VA x MA x nB = VB x MB x nA. standardise an iodine solution.). 25 x MA x 2 = x x 1. Procedure NB: Wear your safety glasses. MA = x / 50 = M. Wash the pipette, burette and conical flask with deionised water. Rinse the student questions pipette with potassium iodate solution Why is hydrated sodium thiosulfate not suitable as a primary and the burette with the sodium standard? thiosulfate a pipette It loses water of crystallisation readily, and it is not stable. filler, fill the pipette with the potassium iodate solution, and transfer the Why are iodine solutions made up using potassium contents of the pipette to the conical iodide solution?