60 g of urea is dissolved in 90 g of water. Then, the mole fraction of solute is

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\frac{5}{6}

\frac{1}{6}

\frac{1}{5}

\frac{4}{5}

answer is B.

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Detailed Solution

Weight of urea

w_{1} = 60 g

GMW of urea $W_{1} = 60 g {.mol}^{- 1}$

Weight of water $w_{2} = 90 g$

GMW of water $W_{2} = 18 g {.mol}^{- 1}$

No.of moles of urea $= n_{1}$

$n_{1} = \frac{w_{1}}{W_{1}} = \frac{60 g}{60 g m o l^{- 1}} = 1 mol$

No.of moles of water $= n_{2}$

$\Rightarrow n_{2} = \frac{w_{2}}{W_{2}} = \frac{90 g}{18 g {.mol}^{- 1}} = 5 mol$

The mole fraction of urea (solute) is,

$χ_{u r e a} = \frac{n_{u r e a}}{n_{u r e a} + n_{w a t e r}}$

Now, we will get,

$χ_{u r e a} = \frac{n_{1}}{n_{1} + n_{2}} = \frac{1}{1 + 5} = \frac{1}{6}$

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