A commercial sample of sulphuric acid has a specific gravity of 1.8. 10 mL of this acid was diluted up to 1 liter with water. 10 mL of diluted acid required 30 mL of N/10 NaOH for complete neutralization. Calculate the percentage purity of H₂SO₄ in the commercial sample.

Solution:

Given:
30 ml of N/10 NaOH was required, 
Applying Normality equation,
N₁V₁ = N₂V₂
N₁V₁ = ( 30 / 1000 ) x (1/10)     ------(i)
Again, 10 ml of diluted acid acid was taken 
N₁ = 30 / 10 x (1/10) 
N₁ = 0.3 
i.e., the normality of diluted acid was 0.3N 
Since,

10 ml of the solution was diluted,

Mass of acid in 10 ml,
mass = NEV /1000 
         =0.3 x ( 98/2 ) x 10 / (1000) 
         = 0.147g 
Since the total solution was of 1 liter, 
Total mass of acid = ( 0.147 / 10 ) x 1000 
                                   = 14.7 g 
Percentage purity (%C) = (real mass / assumed mass) x 100 % 
                                        = ( 14.7 / density x volume )x 100 % 
                                          = ( 14.7 / 1.8 x 100 ) x 100 % 
                                           = 81. 66%