Question

What does CaCl2, MgSO4 or Na2SO4 do? How do you know if you have added enough to the organic layer? What must have occurred if you added MgSO4 to an Erlenmeyer flask containing a colorless solution and it all dissolved?

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Answer 1

CaCl2 , MgCl2 or Na2SO4 all are used as a dehydrating agent or desiccant. They are generally used to remove residual water from organic solvent during work up.

If organic solvent contains water then the solvent have some cloudy nature and if you add the above salt, first the salts absorbs water molecules and the organic solvent become more transparent. This change can predict the water molecules are removed.

If you add MgSO4 to an Erlenmeyer's flask containing a colorless solution and it all dissolved then you can predict that the colour solution is water.