JEE MAIN - Chemistry (2011 - No. 2)
A 5.2 molal aqueous solution of methyl alcohol, CH3OH, is supplied. What is the mole fraction of methyl
alcohol in the solution ?
0.190
0.086
0.050
0.100
Explanation
The formula between Mole fraction and Molality is
$$$m = {{{X_{solute}}} \over {{X_{solvent}}}} \times {{1000} \over {{M_{solvent}}}}$$$
$$m$$ = molality, Xsolute = Mole fraction of solute, Xsolvent = Mole fraction of solvent, Msolvent = Molar mass of solvent
Here solute is methyl alcohol(CH3OH) and solvent is water(H2O). Here water is solvent because question says solution is aqueous.
Assume mole fraction of methyl alcohol = X
So mole fraction of water = 1 - X
and given molality (m) = 5.2
Msolvent = 18 (as molar mass of H2O = 18)
$$\therefore$$ 5.2 = $$ {X \over {1 - X}} \times {{1000} \over {18}}$$
by solving this we get,
X = 0.086
$$m$$ = molality, Xsolute = Mole fraction of solute, Xsolvent = Mole fraction of solvent, Msolvent = Molar mass of solvent
Here solute is methyl alcohol(CH3OH) and solvent is water(H2O). Here water is solvent because question says solution is aqueous.
Assume mole fraction of methyl alcohol = X
So mole fraction of water = 1 - X
and given molality (m) = 5.2
Msolvent = 18 (as molar mass of H2O = 18)
$$\therefore$$ 5.2 = $$ {X \over {1 - X}} \times {{1000} \over {18}}$$
by solving this we get,
X = 0.086
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