Homework Help: CHEMISTRY

Posted by Akle on Saturday, February 18, 2012 at 9:26pm.

A solution of H2SO4(aq) with a molal concentration of 1.94m has a density of 1.119g/mL. What is the molar concentration of this solution?

I got an answer of 2.17 M and it is incorrect..please help.

My work:
So Molar concentration = molal concentration * density
= 1.94 mol/kg * 1.119 kg/L = 2.17 M

CHEMISTRY - DrBob222, Saturday, February 18, 2012 at 10:26pm
Your error is that molar concn x density is NOT molality.

m = moles/kg solvet = 1.94 mol/kg solvent
How much is 1.94 moles H2SO4? That is M x L = 1.94 x 98 = about 190g (remember that's 1.94 mols).
It was dissolve in 1 kg solvent which is 1000 g. It had 190 g (approximate) H2SO4 for a total mass of 1000 +190 = 1190.
mass = volume x density or
volume = 1190 g/1.119 = about 1060 mL or 1.060 L.
So M = moles/L = 1.94 mol/1.063 L = about 1.8 M. You clean up the figures but 1.8 is close to the right answer.
CHEMISTRY - Akle, Saturday, February 18, 2012 at 10:31pm
Thanks so much! :] I understand my mistake!

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