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Molality

When 25g of a...

Question

When 25g of a non-volatile solute is dissolved in 100g of water, the vapour pressure is lowered by 0.225 mm. If the vapour pressure of water at $25^{o} C$ is 17.5 mm, what is the molecular mass of the solute?

200

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300

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350

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250

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Solution

The correct option is C 350
We have,
$\frac{P_{B}^{0} - P_{t}}{P_{B}^{0}} = x_{A}$ = $\frac{n_{A}}{n_{A} + n_{B}}$
on putting the values we have,
$\frac{0.225}{17.5} = \frac{x}{x + 5.55}$
we get x = 0.072
so, molecular weight = $\frac{g i v e n w e i g h t}{n o . o f m o l e s}$

so, molecular weight = 350

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