Question

How many grams of hydrated MgSO4 ⋅ 5 H20 (M.W.: MgSO4 = 119, H20 = 18) are required to make a 10% solution of MgS04

Answer 1

depends on how much solution you want to make.
lets assume one wants a total of 1000g solution. ten percent of that is MgSO4, or 100/119 moles MgSO4. Now if that was previously added as the hydrated salt, then grams of the hydrated salt would have been (100/119)(119+5(18))=177 grams of the hydrated salt added to 1000-177 grams of water.

Answer 2

10% what? 10% w/w? 10% w/v?

I'll make two assumptions here.
1. You want a 10% w/v; i.e., weight/volume
2. You want this to be 10% w/v of MgSO4.5H2O. You flipped between MgSO4.5H2O and MgSO4 in your question.

% w/v = (mass solute/100 mL solution)
10% = [10 g solute/100 solution]

If you want % w/w, it is
%w/w = [(grams solute/total grams solution)]*100
Note: total grams solution means grams of the MgSO4.5H2O + grams H2O

Answer 3

11.9