The
concentration of pollutants in water or atmosphere is often expressed
in terms of mg mL
–1 or ppm (v) Mole fraction: Commonly used symbol for mole fraction is x and
subscript used on the right hand side of x denotes the component It is defined as:
Mole fraction of a component =
Number of moles of the component
Total number of moles of all the components
(1 4)
For example, in a binary mixture, if the number of moles of A and B are
nA and nB respectively, the mole fraction of A will be
xA =

A
A
B
 
n
n
n
(1