Question

How to obtain 3g of 5wt% magnesium sulphate solution?

Answer 1

I don't think you posted the question correctly. If you have a solution of 5% w/w, you simply weigh out 3 grams. I suspect you want to obtain 3g of MgSO4 or 3g of Mg or something like that and you have a solution of 5% w/w. Please rephrase your question.

Answer 2

I have a 5wt% magnesium sulphate solution. I need to dissolve zeolite powder into the solution with the zeolite to salt mass proportion of 20:3. I am confused about the mass proportion of 3 of the magnesium sulphate solution.

Answer 3

The way I read this is as follows:
You have a 5% w/w MgSO4 which is 5 g MgSO4/100 g solution
You want zeolite to be in the ratio of 20:3 zeolite to MgSO4 so if you take 100 g of your 5% solution and add 20 x 5/3 = 33.3 g zeolite the ratio of zeolite:MgSO4 is 20:3. 20:3 is 3 x 6.667 = 20 and 5 x 6.667 = 33.3.
I THINK that's what you mean.