J.R. S. answered 03/04/18
Tutor
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Ph.D. in Biochemistry--University Professor--Chemistry Tutor
30 g of 10% salt soln = 3 g salt + 27 g water
In order to have 20% salt from those 3 g of salt, you need a total mass of 15 g or 3 g salt + 12 g water. So you need to evaporate 15g of water and assuming a density of 1g/ml y would evaporate 15 ml.