posted by CC on .
how would I find the mass of something from the molality.....
How many grams of water should be added to 25.0 g of NaCl to produce a 0.450 m solution?
CC--Definitions, definitions, definitions.
molality = moles/kg solvent
You want 0.45 m and you want 25.0 g NaCl.
How many moles is 25.0 g NaCl? That will be moles = grams/molar mass.
25.0/58.5 (the 58.5 is an estimate) = 0.43 moles. Now substitute that into the definition for molal.
0.45 m = 0.43 mols/kg
solve for kg. (I rounded the 0.43 moles also).
I got it its 950 g