Question

Two liquids, A and B, have vapor pressures at a given temperature of 24 mmHg and 36 mmHg, respectively. We prepare solutions of A and B at a given temperature and measure the total pressures above the solutions. We obtain the following data: Solution Amt A (mol) Amt B (mol) P (mmHg) 30 28 32 2 Predict the total pressure above a solution of 1 mol A and 5 mol B. Express your answer to two significant figures and include the appropriate units

Answer 1

We know according to Raoult's Law for a mixture of liquids A & B Ра 3 ХА РА" and Ps %3D Хв Р3° Here, PA & PB are the partial vapor pressures of the components A and B in the mixture PA & PE are the vapor pressures of the pure individual components A and B. XA & XB are the mole fractions of A and B) of partial pressure, P = PA P The total pressure of the solution will be the sum As given in the solution, there are 1 mol A and 5 mol B so the total number of mol is 6 So, the mole fraction of A, XA 1/6 and mole fraction of B, XB 5/6 Given, PA 24 mm Hg and P 36 mm Hg Then, PA 1/6 x 24 4 mm Hg Рв 3 5/6 х 36 3 30 mm Hg So, total pressure above solution, P = 4 30 = 34 mm Hg