Liquids A and B form an ideal solution at a certain temperature. The vapor press

Question

Liquids A and B form an ideal solution at a certain temperature. The vapor pressures of pure A and B are 450 torr and 732 torr, respectively, at this temperature. a) A sample of solution's vapor is condensed. Given that the original solution contains 3.3 moles of A and 8.7 moles of B, calculate the composition of the condensate in mole fractions. b) Suggest a method for measuring the partial pressures of A and B at equilibrium. I always have trouble understanding the concepts of these questions as well :/

Explanation / Answer

mole fraction calculation :

3.3 moles = A

8.7 moles = B

total moles = moles of A + moles of B = 3.3 + 8.7 = 12

mole fraction of A = moles of A /total moles

                             = 3.3 / 12

                             = 0.275

mole fraction of B = moles of B / total moles

                            = 8.7 / 12

                             = 0.725

note : mole fractions of total components always = 1

B)

pure state pressures

PoA = 450 torr ,    PoB = 732 torr,

partial pressure in the mixture

PA = partial pressure of A

XA .= mole fraction of A

PoA   = pure state pressure

parital pressure of of A= PA = XA .PoA  

                 PA = 0.275 x 450

                      = 123.75 torr

parital pressure of of B= PB = XB .PoB  

                       PB = 0.725 x 735

                            = 532.86 torr

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