Posted by **Marie** on Monday, April 29, 2013 at 11:40pm.

Consider 18.0 M H2SO4, if you need to make 250.0 mL of a 3.0 M solution of H2SO4, how would you do this?

18.0 M H2SO4 has a density of 1.84g/mL what is the molality of solution? Mass % of H2SO4 in the solution and the mol fraction of H2SO4 and water in the solution?

- chemistry -
**DrBob222**, Tuesday, April 30, 2013 at 12:08am
#1.

mL1 x M1 = mL2 x M2

Substitute and solve.

250mL x 3.0M = mL2 x 18

#2.

18.0M means 18.0 mols/L

18.0 mols x (98g/mol) = 1764 grams H2SO4/L solution.

The mass of 1L solution is

1.84 g/mL x 1000 mL = 1840 grams H2SO4 + H2O

%H2SO4 = (mass H2SO4/total mass)*100 = (1764/1840)*100 = ?

mols H2SO4 = 1764/98 = ?

mols H2O = (1840-1764)/18 = ?

total mols = sum

XH2SO4 = mols H2SO4/total mols

XH2O = mols H2O/total mols.

molality = mols/kg solvent. Just substitute the proper numbers.

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- chemistry -
**Marie**, Tuesday, April 30, 2013 at 12:27am
#1 250mL x 3.0 M/18.0M = 41.67mL?

#2 molality of solution???

Mass % 1764/1840x100= 95.87%

Mol fraction...H2SO4. 18/22.2=.81

H2O 4.2/22.2=.18

- chemistry -
**DrBob222**, Tuesday, April 30, 2013 at 4:23pm
#1 looks ok.

#2.

mass % looks ok but if your prof is picky about the number of significant figures I think you need to round that number.

mol fractions look ok except I would have rounded the H2O to 0.19 and not 0.18. In fact, you dropped a 2 from 4.22 and 4.22/22.2 = 0.19

I don't see that you have calculated molality.

That's mols/kg solvent.

You have 18.0 mols and kg H2O = 0.076; therefore, m = 18.0/0.076 = ?

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