[Toxage]

Determine the molarity of the saturated KNO3 solution at 25 Celcius.

I used a graph to determine that 40 grams of KNO3 can dissolve in 100 grams water at 25 Celcius.

40 Grams * 1 Mol     
                ------         = 0.396 Moles --> 0.4 Moles (Sig Figs)
                101 Grams 

Molarity = Moles Solute
             -------------
             Liters Solvent

X = 0.4
      -----
       Y

The problem is I can't use the molarity equation because the solvent is in grams, not liters. I could determine the molality, but there is no way to change molality to molarity. I know of no way to change grams to liters.

[agrobert]

What is the density of water at 25 ºC? Can you convert g to L with this information?

[AWK]

You should find a density of solution in Tables (eg CRC handbook)