# Benzene and toluene form nearly ideal solutions. At 20°C, the vapour pressure of benzene is 75 torr and that of toluene is 22 torr. The parial  vapour pressure of benzene at 20°C for a solution containing 78g of benzene and 46g of toluene in torr is Option 1) 50 Option 2) 25 Option 3) 37.5 Option 4) 53.5

A Abarna

option 1

V Vakul

As we learned

Raoult's Law -

The partial pressure of any volatile constituents of a solution at a given temperature is equal to the product of vapour pressure of pure constituent and its mole fraction in the solution.

$P_{A}=P_{A}^{0}x_{A}$

$P_{B}=P_{B}^{0}x_{B}$

- wherein

$P_{A}^{0}$  and $P_{B}^{0}$ are vapour pressures of pure liquids.

$P_{A}$  and $P_{B}$ are vapour pressures of A and B respectively.

$P_{B}=P_{B}^{0}X_{B};$    $\therefore P_{B}=\frac{\frac{78}{78}}{\frac{78}{78}+\frac{46}{92}}\times 75;$   $\therefore P_{B}=50 torr$

Option 1)

50

Option 2)

25

Option 3)

37.5

Option 4)

53.5

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