Question

How to obtain dry,pure crystals from aqueous sodium sulfate?​

Answer 1

Answer:

Sodium sulfate is a very stable and happy molecule. What it does love is water, which is why it is commonly used in chemistry labs (especially in organic chemistry) to “dry” liquids. I am using the chemistry meaning of dry which is “not containing water”. It is readily hydrated and can be removed from your liquid with a simple filtration.

Sodium sulfite is relatively stable but no where near as stable as the sulfate. It craves that extra oxygen so even if you leave it exposed to air it will slowly oxidize to give sodium sulfate. If you left your aqueous sodium sulfite solution open on the side, atmospheric oxygen would cause the chemical change, the water would hydrate the new compound and the slow evaporation of water would give you lovely large crystals of Na2SO4 without you having to do anything!

If you wanted to speed up this process you could bubble some O2 into a water solution. If you really wanted it to go rapidly I guess you could add an oxidizing agent like hydrogen peroxide. You wouldnt have to worry much about purification either if you did that. You can speed up crystal growth by exposing the sample to a vacuum or cooling it down (not really much good with water!)

I hope this helps!