How to express Concentration of Solutions- 02 – Molarity

Molarity (M))

Molarity (M) is defined as number of moles of solute dissolved in one litre.
Molarity is represented by the symbol M.
Its SI unit is mol.L^-1
When temperature changes, molarity also changes.

Calculation of number of moles when molarity is given.

Molarity when mass of solute and its molar mass is given..

Test Your Self

Q5.1. A flask of volume 625 ml is filled with a solution containing 5 g of Sodium Hydroxide. Find the molarity of the solution.
Q5.2. 49 g of Sulphuric Acid is dissolved in enough water to make 2 L of solutions. Find molarity.
Q5.3. Calculate the molarity of NaOH in the solution prepared by dissolving its 4 g in enough water to form 250 mL of the solution.

What happens when a solution of given molarity is diluted?

If M₁ is molarity of solution and V₁ is its volume before dilution, then total number of moles = M₁V₁.
If M₂ is molarity of solution and V₂ is its volume after dilution, then total number of moles = M₂V₂.
As number of moles does not change,

M₁V₁ = M₂V₂

Q5.4. How much volume of 10 M HCl should be diluted with water to prepare 2.00 L of 5 M HCl.
Q5.5. A bottle contains 35.7 ml of 12.0 M Sulphuric acid. If the acid is diluted to 250 mL, find the concentration of new solution.

Molarity of a solution obtained by mixing two differet solutions of different molarities.

where M₁ and M₂ are molarities of two solutions and V₁ and V₂ are their volumes respectively.
In general,

where M₁, M₂ …. are molarities of solutions and V₁, V₂ … are their volumes respectively.
M_f is molarity of final solution and V_f is volume of final solution obtained.

Q5.6. 200 mL of 2M HCl aqueous solution is mixed with 600 mL of 3.5 M HCl aqueous solution. What is the molarity of final solution?
Q5.7. 3 litres of 5 M KCl solution is mixed with 6 litres of 4 M KCl solution. Find the molarity of resultant solution.
Q5.8. Find the molarity of water if its density is 1000 Kg.m^-3 Answers