Sodium hydrogen carbonate, NaHCO₃

The primary salt is an intermediate product in the ammonia-soda process, and can be prepared by the action of carbon dioxide on a solution of the normal carbonate, preferably in 80 per cent, alcohol.

The salt forms white, monoclinic crystals, of mean density 2.206. On heating it is decomposed:

2NaHCO₃=Na₂CO₃+H₂O+CO₂.

On heating in aqueous solution a similar decomposition takes place:

NaHCO₃+H₂O = NaOH+H₂O+CO₂;

NaHCO₃+NaOH =Na₂CO₃+H₂O.

The heat of formation of the salt from the elements is given as 229.3, 228.38, and 227.0 Cal. The solubility-data given by Dibbits are summarized in the table:

Temperature, °C	0	10	20	30	40	50	60
Grams NaHCO3 in 100 g. water	6.9	8.2	9.6	11.1	12.7	14.5	16.4

Its solution in water has a faint alkaline reaction. In presence of steam, sodium hydrogen carbonate is converted by sodium sulphide into the normal carbonate:

2NaHCO₃+Na₂S =2Na₂CO₃+H₂S.

The constitution of the primary carbonate is represented by Bicher by the bimolecular formula Na₂CO₃,H₂CO₃ or


A double salt with the normal carbonate, Na₂CO₃,NaHCO₃,2H₂O, occurs in Venezuela as Urao, and in Egypt as Trona. It is formed on concentrating a solution of the two salts in molecular proportions, and has been observed to be a product of the efflorescence of the normal decahydrate during a period of twenty years.