question_answer 48)

100 g of liquid A (molar mass 140 g mol-1) was dissolved in 1000 g of liquid B (molar mass 180 g mol-1). The vapour pressure of pure liquid B was found to be 500 torr. Calculate the vapour pressure of pure liquid B was found to be 500 torr. Calculate the vapour pressure of pure liquid A and its vapour pressure in the solution if the total vapour pressure c' the solution is 475 torr.

Answer:

No. of moles of liquid A (nA) No. of moles of liquid B    Mole fraction of A in the solution (xA)  Mole fraction of B in the solution (xB) = (1 ? xA) = 1 ? 0.114 = 0.886 Also, given   Applying Raoult's law,                    ?? (i)           =  443 torr                            ... (ii) PTotal = 0.114    or   (Vapour pressure of pure liquid A) Substituting this value in equation (i), we get PA (Vapour pressure of A in solution) = 0.114 x 280.7 torr = 32 torr