CHAPTER THREE "SOLUTIONS"
Solution may be gaseous , liquid or solid is a homogeneous mixture of two or more
substances .It is a single phase.
Vapour pressure is a measure of mutual attraction of particles in a liquid.This is the pressure
of that liquid which is in equilibrium with its liquid at constant temperature.
Raoults law:states that the relative lowering of the vapour pressure of a solvent due to the
addition of a solute is equal to the molecular fraction of the solute in the solution.imagine
two substances A and B forming a solution. Each substance exerts its own vapour pressere ,
pA and pB respectively
THEN
This means that if the solution obeys raoults law the vapour pressure of one of the
components of that solution is directly proportional to the mole fraction of that component
in the solution.
An ideal solution :the molecules of A and B must be of similar size and must attract one
another with the same force as molecules of B attract other molecules of B or molecules of A
attract other molecules of A and also the vapour should behave as an ideal gas for the
solution to obey raoults law.
If A attract B more strongly than the mutual attraction of A or of B molecules then in the
solution of A andB ,neither A nor B tend to leave the liquid and the vapour pressure exerted
by each component of the solution will be lower than that expected if the solution was
ideal.This lead to a negative deviation from raoults law.
If the attraction between A and B molecules is weaker than the mutual attraction of A
molecules or B molecules , then in solution the molecules will leave the surface of the liquid
more easily than would be expected for an ideal solution.the vapour pressure will higher and
there will be a positive deviation from raolults law.