Calculate the molality of a 1.5 M aqueous salt solution in a solvent X, if the mole fraction of the salt in the solution is 0.25.
(Molar mass of solvent = 40 g/mol)
A
18.52m
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B
12.85m
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C
8.33m
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D
15.24m
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Solution
The correct option is C8.33m 1.5 molar solution means 1.5 mol of soluble salt is present in 1 L of the solution. Molefractionofsolute=xsolute=molesofsolutemolesofsolute+molesofsolvent
⇒ 0.25=1.51.5+nX
On solving,
Moles of solvent X =nX=4.5mol
Weight of solvent =4.5×40=180g Molality(m)=molesofsolutemassofsolventing×1000 Molality=1.5180×1000=8.33m