Benzene and toluene form nearly ideal solutions. At 20^{\circ}C the vapour pressure of benzene is  75 torr and that of toluene is 22 torr. The partial vapour pressure of benzene a 20^{\circ}C for a solution containing 78 g of benzene and 46 g of toluene in torr is

  • Option 1)

    50

  • Option 2)

    25

  • Option 3)

    37.5

  • Option 4)

    53.5

 

Answers (1)

As we learnt in

Rault's Law -

The total vapour pressure of binary mixture of miscible liquids be having ideally is given by

P_{T}= P_{A}^{0}x_{A}+P_{B}^{0}x_{B}

Where x_{A}  and  x_{B} are mole fraction of A and B in liquid phase.

 

 

- wherein

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

 

 

According to Raoult's law ,P_{B}= P^{0}_{B}X_{B} \; \; \; \; \; \; P^{0}_{B}= 75\: torr

X_{B}= \frac{78/78}{\left ( 78/78 \right )+\left ( 46/92 \right )}= \frac{1}{1+0.5}= \frac{1}{1.5}

P_{B}= 75\times \frac{1}{1.5}= 50 \; torr

Correct option is 1.

 


Option 1)

50

This is the correct option.

Option 2)

25

This is an incorrect option.

Option 3)

37.5

This is an incorrect option.

Option 4)

53.5

This is an incorrect option.

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