[mrjon]

Hello, I'm trying to make a solution that has a 30% concentration of MgCl2 by weight. I need 72 kg of this solution. When I bought the MgCl2, the formula in the bottle says MgCl₂·6H₂O. Having this extra water will dilute my solution, so how much of this do I need to add to water to ensure that I have 30% concentration of MgCl2?

Thanks for the help.

[kreysiz]

Total mass of solution required = 72 kg = 72000 g
Mass of MgCl2 required = 305 of the mass of solution = 0.3*72000 = 21600 g
Now, Molar mass of MgCl2.6H2O = 203 g/mole
molar mass of MgCl2 = 95 g/mole
Thus, moles of MgCl2 required = mass of MgCl2/molar mass of MgCl2 = 21600/95 = 227.368
Thus, moles of MgCl2.6H2O required = moles of MgCl2 = 227.368
mass of MgCl2.6H2O required to be added = moles of MgCl2*molar mas of MgCl2 = 227.368*203 = 46155.789 g
Hence mass of water required = 72000 - 46155.789 = 25844.211 g