Sodium Carbonate is also called as Soda Ash.  

Characteristics: Soda ash is a white, odorless, hygroscopic powder, with an alkaline taste. It is soluble in water and glycerin, insoluble in alcohol.

Assay:  About 5 g of sample accurately weighed, is dissolved in carbon dioxide free water and made up to 1 liter. 50 ml is then titrated with 0.1 N hydrochloric acid, first in the presence of phenolphthalein till the pink color is discharged and then in the presence of methyl orange till an orange tint is obtained.

Let x = ml of 0.1 N acid used in the first titration,

y = ml of 0.1 N acid used in the second titration, and

w = wt of sample in aliquot in g.

Then if x > y, Na₂CO₃ and NaHCO₃ are present and given by

Na₂CO₃, % = 2y x 0.0053 x 100

w

NaHCO₃, % = (y- x) x 0.0084 x 100

w

Reactions:

Na₂CO₃ + HCl                               NaHCO₃ + HCl

NaHCO₃ + HCl                               NaCl + H₂O + CO₂

NaOH + HCl                                  NaCl + H₂O