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**1. For a problem I require the atomic density of uranium atoms per cm^3 in a solution of water. The atomic fraction of natural uranium to water is 1 per 100 and the net density of the solution is 1 g/cm^3. (Natural uranium is assumed to be U-235 at 0.72% of uranium atoms and the rest is U-238) (assume the atomic weights of U-235, U-238 and water are 235, 238 and 18 respectively)**

What I require is the atomic density of U-235 atoms, the atomic density of U 238, and H2O atoms all in atoms/cm^3.

I have tried to calculate the overall atomic weight of the solution weighted by the atom concentration as in:

0.000072(235) + 0.009928(238) + 0.99(18) = 20.35 g/mol?

then since the solution has net density 1 gm/cm^3:

1 / 20.35 = 0.049 mol/cm^3

then using avogadro's number convert to atoms/cm^3, then use the 1 in 100 again to find how many are U235, U238, water....is this a correct method. something seems wrong in this.

thanks for the help