Question

2 liquids X and Y on mixing form an ideal solution.At 30 degree celsiusthe vapour pressure of the solution containing 3 moles of X and 1 mole of Y is 550 mm of Hg.But when 4 moles of X and 1 mole of Y are mixed,the vapour pressure of the solution thus formed is 560 mm of Hg.What would be the vapour pressure of pure X and pure Y at 36 degree Celsius this temperature ?

Answer 1

according to Dalton's law of partial pressure.

Ptotal=Px+Py

we also know, partial pressure of each component of the solution is directly proportional to mole fraction of of it.

e.g., Px=xPx°

case 1 :- mole fraction of X = 3/(3 + 1) = 3/4

mole fraction of Y = 1/(3 + 1) = 1/4

we know, Pressure of solution = pressure of X + pressure of Y

550mm=xP°x+yP°y

550mm = 3/4P°x + 1/4P°y .......(i)

similarly,

case 2 :- mole fraction of X = 4/5

mole fraction of Y = 1/5

now, 560mm=x¹P°x+y¹P°y

560mm = 4/5P°x + 1/5P°y........(ii)

after solving equations (i) and (ii) we get ,

Px°=600mmHg

and

Py°=400mmHg