Relationship between Normality and Molarity of Solutions

Normality and Molarity are related as:

For acids

Normality = Molarity x Basicity

where basicity is the number of H⁺ ions a molecule of an acid can give.

For bases

Normality = Molarity x Acidity

where acidity is the number of OH^- ions a molecule of a base can give.

Problems

14. Commercially available concentrated hydrochloric acid contains 38% HCl by mass.

(a) What is the molarity of this solution? The density is 1.19 g/mL.

(b) What volume of concentrated HCl is required to make 1.00 L of 0.10 M HCl?

Solution

(a) 38% solution, means 38 g of HCl in 100 g of solution.

Then, Mass of the solution= 100 g

Molar mass of HCl = 36.5 g mol^-1

(b) The molarity of conc. HCl sample = 12.38 mol/L

Molarity of HCl solution to be prepared = 0.10 mol/L

Volume of HCl solution to be prepared =1.00 L= 1000mL

Then, using molarity equation, M₁V₁ = M₂V₂

Thus, to obtain 1.0 L of 0.10 M HCl, one should dissolve 8.08 mL of concentrated HCl to make up the volume to 1.0L.

15. Concentrated nitric acid used as a laboratory reagent is usually 69% by mass of nitric acid. Calculate the volume of the solution which contained 23 g HNO₃. Density of the concentrated HNO₃ solution is 1.41 g cm^-3.

Solution

Let, mass of conc. HNO₃ sample = 100g

Mass of HNO₃ in 100 g of sample = 69 g

Mass of water in 100 g of sample = 31 g

Density of conc. HNO₃ sample = 1.41 g cm^-3

= 70.92 cm³

Thus, 69 g of HNO₃ is contained in 70.92 cm³ of conc. HNO₃

Thus 23.6 cm³ concentrated HNO₃ sample contained 23 g of HNO₃.