Mole Concept in Solutions

A solution is defined as a homogeneous mixture of two or more chemically non reacting substances, the relative amount of which can be varied up to a certain limit.

If a solution consist of only two components it is called a binary solution.

The component present in smaller amount is called solute while the other present in larger amount is called solvent

The concentration of the solution can be expressed in number of ways:

(1) Mass percent or weight percent :Mass percent of a solute in a solution is the mass of the solute in grams present in 100 grams of solution.

(2) Strength: Strength of a solution is defined as the amount of the solute in grams present per litre of the solution.

(3) Molarity: Molarity of a solution is defined as the number of moles of the solute present per litre of the solution.It is represented by the symbol, M.

(4)​ Molality :The molality of a solution is defined as number of moles of the solute dissolved in 1 kg of the solvent.

 

It is represented by the symbol m.

(5) Normality : Normality of a solution is defined as the number of gram equivalent of the solute present per litre of the solution.

It is represented by the symbol N.

Basicity is the number of displaceable H⁺ ions present in 1 molecule of the acid.

Acidity is the number of displaceable OH^– ions present in 1 molecule of the base.

(6) Mole fraction : Mole fraction of any component in the solution is equal to the number of moles of that component divided by the total number of moles of all the components.

For a solution containing n₂ moles of the solute dissolved in n₁ moles of the solvent,

(7) Parts per million: The concentration of very dilute solution is expressed in terms of parts of the solute by mass present in million parts by mass of the solution.

Molarity equation

If a solution having molarity M₁ and volume V₁ is diluted to volume V₂ so that the new molarity is M₂ then as the total number of moles in the solution remains the same, we have :

Normality Equation

Relation between molarity and normality of the solution of an acid or base

Normality of solution of an acid = Molarity × Basicity

Normality of solution of a base = Molarity × Acidity

Calculation of Molarity and Normality of the solution obtained on mixing two or more solution

If the solutions mixed are of the same substance 

If V₁ mL of a solution of molarity M₁ are mixed with V₂ mL solution of the same substance with molarity M₂ Or V₁ mL of M₁ HCL solution are mixed with V₂ mL of M₂ , then the molarity of the solution obtained is calculates as:

M₁ V₁ + M₂ V₂ = M₃ (V₁ +V₂)

N₁V₁ + N₂V₂ = N₃ (V₁ +V₂)