What is the hardness of water containing 1% w / w magnesium sulfate?

Given:
ω (MgSO4) = 1%
ρ solution = 1 g / cm3 = 1 g / ml

To find:
F total. (H2O) -?

Decision:
1) Let V solution = 1 l = 1000 ml;
2) Calculate the mass of the solution:
m solution = ρ solution * V solution = 1 * 1000 = 1000 g;
3) Calculate the mass of MgSO4:
m (MgSO4) = ω (MgSO4) * m solution / 100% = 1% * 1000/100% = 10 g;
4) Calculate the equivalent mass of MgSO4:
M eq. (MgSO4) = M (MgSO4) / (N (Mg) * valence Mg) = 120 / (1 * 2) = 60 g / mol;
5) Calculate the water hardness:
F total. (H2O) = m (MgSO4) / (Meq (MgSO4) * V solution) = 10 / (60 * 1000) = 0.17 mmol / L.

Answer: Water hardness is 0.17 mmol / l.