LIQUID SOLUTION
(a) Percent by weight
(b) Percent by volume
(g) Normality
(h) ppm
%by
weight of solute 
For example, if a solution of HCI contains 36 % HCI by weight, it has 36 g of HCI in 100 g of solution.
For example, it we have 35% C2H5OH solution by volume means 25 ml C2H5OH is present per 100 ml of the solution.
Notice that mole fraction of solvent would be
8.1.5 Molarity (M)
In current practice, concentration is most often expressed as molarity. Molarity is defined as the number of moles of solute per litre of solution.
8.1.6 Molality (m)
Molality of a solution is defined as the number of moles of solute per kilogram of solvent:
8.1.7 Normality (N)
Normality of a solution is defined as number of equivalents of solute per litre of the solution:
8.1.8 ppm (parts per million)
It is the mass of solute in grams present per 106 grams of solution.
8.2 Vapour Pressure
The molecules of the liquid which possess high kinetic energy have a tendency to change to vapour state. When a liquid is placed in a closed container then due to evaporation, vapours of liquid are produced which ultimately leads to an equilibrium state due to the tendency of the vapours to convert back to liquid. The pressure exerted by the vapours of the liquid which are in equilibrium with the liquid phase at the given temperature, is known as vapour pressure.
When the intermolecular forces of attractions are stronger then the vapour pressure will be low because less number of molecules can leave the liquid.
Out of C2H5OH, CH3OCH3, CH3CHO the one with highest vapour pressure is CH3OCH3 and the one with lowest vapour pressure is C2H5OH because in C2H5OH there is hydrogen bonding leading to strongest intermolecular forces where as in CH3OCH3 there is Vander Waals forces leading to weakest intermolecular forces.
Psolution = PA + PB
Where PA and PB are the partial vapour pressures of A and B.
PºA and PºB are vapour pressures of pure A and B respectively.
cA and cB are mole fraction of A and B in liquid solution respectively
or 
Similarly for B
Mixing of Two Immiscible Liquid
Let us consider the case of mixing of two volatile but immiscible liquids A and B. In the mixture of two liquids, if P0A and P0B are vapour pressures, of two liquids in pure state, then according to Dalton’s law, total vapour pressure is given by
similarly |
Vapour composition
similarly
Also
= mass of
B
= molecular mass
of B
To comply to this condition for ideality the two liquids A and B should fulfill the under mentioned conditions
1. The attractive forces between the particles A and B (i.e. A–B interactions) should be equal to the attractive forces between A and A (i.e. A–A interaction) and between B and B (i.e. B–B interaction)
8.4 Binary Non Ideal Solutions
Non-Ideal Solution with Negative Deviation
The B set of solutions show a relationship where the vapour pressure of solution observed is lesser than the vapour pressure of the solution under ideal conditions i.e.
Then the heat energy released when A–B interaction take place will be more than compared to the heat energy required for breaking the A–A interaction or B–B interactions. Hence the net result is DHmix < 0 Þ DHmix = –ve and also |
8.5 Colligative Properties of Solution
When a non volatile solute is present in the solution, the vapour pressure of the solution will be less than vapour pressure of pure solvent.
Lowering in vapour pressure is directly proportional to the mole fraction of solute.
For
dilute solutions n << N, hence 
\ 
W = Mass of solvent in grams
m = Molecular mass of solute
8.5.2 Elevation in Boiling Point
When a liquid is heated then due to rise in temperature the liquid vapourises and the vapour pressure increases. When the vapour pressure of the liquid becomes equal to the atmospheric pressure, the liquid begins to boil. The temperature at which the equilibrium vapour pressure of the liquid becomes equal to the atmospheric pressure is called boiling point.
If T0 is the boiling point of solvent and T1 is the boiling point of solution, then
Kb = Molal elevation constant
At freezing point liquid and solid are in equilibrium. At the freezing point the vapour pressure of liquid and solid will be same. |
DTf = Kf × m
Kf = 
pV = nRT
p = CRT
8.6 Abnormal Behaviour of Solutions
To account for the above anomalies, Van’t Hoff
introduced a factor ‘i’ in the Van’t Hoff equation
(p V = RT) of osmotic pressure.
The modified equation may thus be written as pV = iRT
The factor ‘i’ was defined by the expression
Hence ‘i' can also be defined as
(b) Elevation in Boiling point
DTb = iKb m