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InterviewSolution
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Why is sodium thiosulphate not considered as a primary standard? |
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Answer» Sodium thiosulphate comes as a nominal pentahydrate. But it is quite difficult to ascertain the water of crystallization, as the exact composition of the pentahydrate is highly dependent on temperature and humidity.In simpler words, when the humidity is high the crystals absorb water and at lower humidity and higher temperature there is loss of water of crystallization.We can thus not know exact composition to get an exact molecular weight. Without exact molecular weight one cannot prepare a standard solution. |
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