Q

Tell me? - Some basic concepts in chemistry - JEE Main-2

The mole fraction of a solvent in aqueous solution of a solute is $0.8.$ The molality $\left ( in\: \: \: mol\: Kg^{-1} \right )$  of the aqueous solution is :

• Option 1)

$13.88\times 10^{-2}$

• Option 2)

$13.88\times 10^{-3}$

• Option 3)

$13.88\times 10^{-1}$

• Option 4)

$13.88$

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Mole Fraction -

It is ratio of moles of solute or moles of solvent to moles of solution.

- wherein

If a substance ‘A’ dissolves in substance ‘B’ and their number of moles are $n_{A}$ and $n_{B}$ respectively; then the mole fractions of A and B are given as

Mole fraction of A = (number of moles of A)/(number of moles of solution ) = $n_{A}$/($n_{A}$+ $n_{B}$)

We have,

$mole\: \: fraction=0.8$

$X_{solvent}=\frac{n_{solvent}}{n_{solute}+n_{solvent}}=\frac{0.8}{1}$

$n_{solute}=0.2mole$

$molality=\frac{0.2}{0.8\times 18}\times 1000$

$=13.88$

Option 1)

$13.88\times 10^{-2}$

Option 2)

$13.88\times 10^{-3}$

Option 3)

$13.88\times 10^{-1}$

Option 4)

$13.88$

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