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In the reaction between sodium thiosulphate and sulphuric acid according to the written equation, solid sulphur happens to be a product of the reaction. I have also noticed that at the end of the reaction there is a very pungent odour which I deduced to be sulphur. I also thought that sulphur was a yellow pigment but at the end of the reaction the solution is transluscent or somewhat opaque, but not yellow - it seemed to be more cloudy than yellow. What explanation is there to this?
Corrie writes ....
The very pungent odour you are detecting is sulphur dioxide, a very soluble gas also produced in this reaction.
As for the solid sulphur, I am not surprised by what you described. The finely divided precipitate of sulphur is not very yellow at first, and makes the solution look milky, slight off-white, rather than yellow. This does not affect the experiment.
If you let the solid sulpur coagulate into larger particles of solid over a period of time (preferably in a fume cupboard because of the smell!), you will notice a more yellow colour developing, especially if the sulphur settles to the bottom.
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updated: 08 November 2007
