Question

7. Consider the expression of Raoult's law,

P_solution = X_solvent ·P^⁰_solvent .

Here,

P_solution = vapor pressure of the solution,

P^⁰_solvent  = vapor pressure of pure solvent,

X_solvent  = mole fraction of the solvent.

What is the mole fraction of solvent in a solution with a vapor pressure of 47.90 torr, if the vapor pressure of the pure solvent is 52.82 torr?

8. The boiling point of a solution increases directly as a function of the number of moles of solute present in a given mass of solution. This relationship is expressed mathematically by the following equation.

ΔT_b = K_b·m

ΔT_b is the boiling-point elevation of a solution, m is the molality of solute particles in solution, and K_b is the molal boiling-point-elevation constant.

Determine the number of moles of sucrose present in a 11.70 g sample of water that has a boiling point of 102.33°C. The boiling point for pure water is 100.00°C and the molal boiling-point-elevation constant for water is 0.51°C/m.

Answer 1

Ans 7 :

P_solution = X_solvent ·P^⁰_solvent 

P solution = 47.90 torr

P^o solvent = 52.82 torr

putting values :

47.90 torr = X solvent x 52.82 torr

X solvent = 0.907

So mole fraction of solvent will be 0.907