posted by Cece .
How many kilograms of H2O must be added to 76.0 g of Ca(NO3)2 to form a 0.509 m solution?
m stands for molality; I'm assuming that's what you mean.
mols Ca(NO3)2 = 76g/molar mass = ?
Then m = mols solute/kg solvent
m = 0.509 = ?mol/x kg
?mols from above.
Solve for x kg.