Question

Total vapour pressure of a mixture of 1 mole A`("p"_"A"^circ = 150 " torr")` and 2 mole B`("p"_"B"^circ = 240 " torr")` is 200 mm. In this case, ______.

पर्याय

• there is a positive deviation from Raoult’s law.

• there is a negative deviation from Raoult’s law.

• there is no deviation from Raoult’s law.

• molecular masses of A and B are also required.

Answer 1

Total vapour pressure of a mixture of 1 mole A`("p"_"A"^circ = 150 " torr")` and 2 mole B`("p"_"B"^circ = 240 " torr")` is 200 mm. In this case, there is a negative deviation from Raoult’s law.

Explanation:

`"P"_"s" = "p"_"A"^circ "X"_"A" + "p"_"B"^circ "X"_"B"`

`"P"_"s" = (150 xx 1)/3 + (240 xx 2)/3   ... [("X"_"A" = 1/(1 + 2) = 1/3),("X"_"B" = 2/(1 + 2) = 2/3)]`

P_s = 50 + 160

P_s = 210 torr

But `"P"_"s" = "p"_"A"^circ "X"_"A" + "p"_"B"^circ "X"_"B"`

= 210 mm > 200 mm

Vapour pressure is decreased. So, there is a negative deviation from Raoult's law.