What Size is the Right Size?
Today in class, we examined practice example 2.6 with a 0.30 mass fraction of
H2SO4(aq) whose density was given as 1.218 g/ml.
Route:
Mass fraction (given concentration unit):
O
H
mass
SO
H
mass
SO
H
mass
2
4
2
4
2
30
.
0
+
=
We assumed 1L of solution and used density to convert 1L to 1.218e3 grams.
We then determine that the solution is composed of 365.4g H2SO4 and 852.6 g H2O.
Convert these to mols to obtain 3.73 mols H2SO4 and 47.4 mols H2O
Calculate a mol fraction of H2SO4 = 0.073 or a 7.3 mol percent.
Another “convenient” sized sample would be 100g.
Why?
If the mass fraction is 30%
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 Fall '07
 Warren
 Chemistry, Kilogram, mass fraction, Mol fraction, mol percent

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