Sodium Carbonate

Sodium Carbonate
Chemical FormulaNa2CO3
Formula Weight105.99
Equivalent Weight52.99 (Molar = 2 Normal)
CAS No.497-19-8

Sodium Carbonate is used as a basimetric standard but it is not a very good primary standard since it is difficult to dry, is hygroscopic, and has a relatively low equivalent weight. For these reasons, Tris(hydroxymethyl)aminomethane has largely replaced it as a basimetric standard. Sodium Carbonate is a diequivalent base and it can be assayed by titration with a standard strong acid to the first equivalence point (pH ~ 8.3) using Phenolphthalein Indicator, or to the second equivalence point (pH ~ 3.7) using Methyl Orange Indicator. Reactions involved using Hydrochloric Acid as titrant are:

Na2CO3 + HCl → NaHCO3 + NaCl (first endpoint)

NaHCO3 + HCl → H2CO3 + NaCl (second endpoint)

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