What is the reason of using iodine rarely as primary standard for the standardization of thiosulfate...

What is the reason of using iodine rarely as primary standard for the standardization of thiosulfate solution?

Expert Solution

Solution:

Two most important solutions used in iodometric titrations are solution of iodine and solution of sodium thiosulfate. Both substances can be easily obtained in a pure form, but their other characteristics make them difficult to use as a primary standards. It is also worth of mentioning that both solutions are not quite stable and they can not be stored for a prolonged period of time. Iodine can be lost from the solution due to its volatility, while thiosulfate slowly decomposes giving off elemental sulphur. Iodine is rarely used as a primary standard for thiosulphate because it presents a problem in weighing and maintaining its solution concentration.Due to its volatility,iodine is difficult to weight accurately, as it tends to run away. To minimize losses it should be weight in closed weighing bottle and also require to transfer iodine to the solution as fast as possible. Solution should be kept in dark glass bottle with grinded glass stopper and standardized every few weeks or before use.

queen_honey_blossom answered 2 years ago

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