Question
For a dilute solution, Raoult’s law states that :
A.
the lowering of vapour pressure is equal to the mole
fraction of solute.
B.
the relative lowering of vapour pressure is equal to the
mole fraction of solute.
C.
the relative lowering of vapour pressure is proportional
to the amount of solute in solution.
D.
the vapour pressure of the solution is equal to the mole fraction of solvent.
Answer :
the relative lowering of vapour pressure is equal to the
mole fraction of solute.
Solution :
$$\frac{{{p^ \circ } - p}}{{{p^ \circ }}} = \frac{{\frac{w}{m}}}{{\frac{w}{m} + \frac{W}{M}}} = {\text{mole fraction of solute}} = {x_B}$$
[ Mathematical statement of Raoult's law ]