Question

A 2.0 g sample of a mixture containing sodium carbonate, sodium bicarbonate and sodium sulphate is gently heated till the evolution of CO₂ ceases. The volume of CO₂ at 750 mm Hg pressure and at 298 K is measured to be 123.9 mL. A 1.5 g of the same sample requires 150 mL of (M/10) HCI for complete neutralization. Calculate the percentage composition of the components of the mixture.

Answer 1

According to ideal gas equation,

On heating a mixture of NaHCO₃,Na₂CO₃ and Na₂SO₄, only NaHCO₃ is decomposed according to following equation.

Thus, the weight of NaHCO₃ in the mixture = 0.84

Hence, the percentage of NaHCO₃ in the mixture

= 0.84/2.0 x 100 = 42.0 %

When 1.5 g of mixture is treated with HCl. Therefore, Na₂SO₄ is not reacted while Na₂CO₄ is reacted with HCI as follow :

Suppose, the amount of Na₂CO₃ in 1.5 g of mixture is.y g.

So, the amount of HCl used with Na₂CO₃ = 73/106 x y g

NaHCO₃ reacts with HCl as follows :

Thus, percentage of Na₂SO₄ in the mixture = 100 -% of NaHCO₃ - % of  Na₂CO₃ = 100 - 42 - 26.5 = 31.5 %