**Unit of concentration of solution:**

**Molarity*** (M)***: **Molarity of a solution is the number of moles of solute dissolved per litre of solution. Thus,

Molarity (M) = Number of moles of solute/Volume of solution in litres

If **W _{A} **gram of solute is present in

**V**ml of a given solution, then-

Molarity (M) = (W_{A/Molar mass} x1000/V)

**Molality*** (m):* Molality is the number of moles of the solute dissolved per l000g (or 1 kg) of the solvent. It is denoted by** m. **Therefore,

Molality (m) =Number of moles of solute/Mass of solvent in 1 kg or l000g

If **W _{A} **gram of solute is present in

**W**gram of solvent, then

_{B}Molality (m) = (W_{A/Molar mass} x1000/W_{B})

**Mole Fraction*** (X):*

Mole fraction is the ratio of number of moles of solute or solvent to the total number of moles present in the solution. It is denoted by **X**. Let us consider** n _{A}** and

**n**be the number of moles of A and B present in solution. Then,

_{B}Mole fraction of solute A, X_{A} = n_{A /} (n_{A }+ n_{B)} ————– (1)

Mole fraction of solute B, X_{B} = n_{B} / (n_{A }+ n_{B)} ————– (2)

Adding expression (1) & (2), we have

X_{A }+ X** _{B}** = n

_{A / (}n

_{A }+ n

_{B}) + n

_{B}/ (n

_{A }+ n

_{B)}=1

Therefore, sum of mole fractions of all the components in solution is always equal to one.

**Normality **(N): Normality of a solution is the number of gram equivalent of solute dissolved per litre of the given solution. Therefore,

Normality (N) =Number of gram equivalent of solute/Volume of solution in litres

If **W _{A} **gram of solute is present in

**V**ml of a given solution, then

_{ }Molality (m) = W_{A} /Eq. mass x_{ }1000/V

**Percentage **(%): The mass percentage of a component in a given solution is the mass of the component per 100g of the Solution. The % may be express in the following ways:

- (w/w) %
- (w/v) %
- (v/w) %
- (v/v) %

**Raoult’s Law for solution containing non-volatile solute**:

According to Raoult’s law, at a given temperature, the vapour pressure of a solution containing non-volatile solute is directly proportional to the mole fraction of the solvent. If **P _{A}** is the vapour pressure of a solution containing non-volatile solute and

**X**is its mole fraction. Then,

_{B}P_{A} α X_{B}

Or, P_{A} = K X_{B} Where, K = Proportionality constant.

For pure solvent, X_{B} = 1, then K becomes equal to vapour pressure of pure solvent which is denoted by P°_{A} Therefore,

P_{A} = P_{A}° X_{B} **(**P_{A} = P_{A}°**)**