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Topic: Molality (Concentration)  (Read 2821 times)

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Offline devvaibhav

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Molality (Concentration)
« on: June 11, 2011, 09:52:11 AM »
Q:- What is the molality of 98% H2SO4 by weight?

An approach to solution:- Let we took 100 g of H2SO4 solution. It means that we have 98 g H2SO4 in the solution. Let us assume the solvent to be Water (H2O). So the water comes out to be 2 g.


Wt. of solute (H2SO4) = 98 g
Mol. wt. of solute (H2SO4) = 98 g
Wt. of solvent(H2O) = 2 g

Now according to formula of molality:-   
(98*1000) / (98*2)= 500

But it is incorrect...

Again let us go to the definition of solute and solvent:
Solute: It is present is smaller amount, and
Solvent: It is present is greater amount.
But here we assumed the H2SO4 to be solute which is 98 g and H2O to be solvent which is 2 g.

Let us find the solution by assuming H2SO4 as solvent and H2O as solute.

Wt. of solute(H2O) = 2 g
Mol. wt. of solute(H2O) = 18 g
Wt. of solvent(H2SO4) = 98 g

According to formula: (2*1000) / (18*98) = 1.13

Both the answers are wrong as the answer is 10 m.

If in first case
Wt. of solute (H2SO4) = 98 g
Mol. wt. of solute (H2SO4) = 98 g
Wt. of solvent(H2O) = 2 g, we change it to
Wt. of solution = 100 g

(98*1000) / (98*100) = 10 m but How??

Where am i wrong??please tell me...

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Re: Molality (Concentration)
« Reply #1 on: June 11, 2011, 10:40:33 AM »
By my book 500 is a correct answer.

10m solution is 49.5% w/w
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