Calculate the mass of solid neded to make 500ml of solution that is 0.25m in sulfate ion, using sodium sulfate decahydrate.

Answer 1

I ASSUME that is 0.25M and not 0.25m. M means molarity. m means molality.
How many moles do you need? That will be M x L = 0.500 x 0.25M = ?
moles Na2SO4.10H2O = grams/molar mass.

Answer 2

40