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Solutions Part 1

Section: Chemistry

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Question : 90 of 100

Marks: +1, -0

Benzene and toluene form nearly ideal solutions. At

20^{\circ} \, \mathrm{C}

, the vapour pressure of benzene is 75 torr and that of toluene is 22 torr. The partial vapour pressure of benzene at

20^{\circ} \, \mathrm{C}

for a solution containing

78 \, \mathrm{g}

46 \, \mathrm{g}

of toluene in torr is

$50$
$25$
$53.5$
$37.5$

Solution:

Given, Vapour pressure of benzene

=75 \, \mathrm{torr}

Vapour pressure of toluene

=22 \, \mathrm{torr}

mass of benzene in

=78 \, \mathrm{g}

hence moles of benzene

=\frac{78}{78}=1

mole

(\mathrm{mol}

. wt of benzene

=78)

mass of toluene in solution

=46 \, \mathrm{g}

hence moles of toluene

=\frac{46}{92}=0.5

mole

Total moles of benzene and toluene

=1.5 \, \mathrm{mol}

now partial pressure of benzene

=P_b^{\circ} \times X_b = 75 \times \frac{1}{1+0.5}

=75 \times \frac{1}{1.5} = 75 \times \frac{2}{3} = 50

torr

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