Why Is Baking Soda Called Sodium Bicarbonate?

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Why baking soda is called sodium bicarbonate
Baking soda is sodium bicarbonate. There is a “bi” in sodium bicarbonate because of an archaic naming system. Sodium bicarbonate produces twice as much (bi) carbonate per sodium ion as sodium carbonate. The IUPAC prefers the name sodium hydrogen carbonate, but the old name persists.

Baking soda is called sodium bicarbonate or bicarbonate of soda, depending on your country of origin. However, there is only one carbonate ion in the compound. Here’s the explanation for why baking soda is sodium bicarbonate (when it’s really not) and a look at a better name for the compound.

Sodium Bicarbonate vs Sodium Carbonate

If you’re asked to write the chemical formula for sodium bicarbonate based on its common name, you’ll likely get it wrong. You know the sodium cation (Na+) has a +1 charge and the carbonate anion (CO32-) has a -2 charge, so you’d probably write something like Na4(CO3)2, which balances the charge, but isn’t correct. If you reduce the subscripts to get Na2CO3, you get an altogether different compound.

The formula for sodium bicarbonate is NaHCO3. There is another compound called washing soda or sodium carbonate, which has the formula Na2CO3. Heating baking soda drives off the hydrogen and gives you washing soda. Dissolving baking soda yields one sodium ion and one bicarbonate anion (HCO3–). Dissolving washing soda gives you two sodium ions and one carbonate ion (CO32-).

Why Baking Soda Is Called Sodium Bicarbonate

Baking soda and washing soda were widely used long before their chemical formulas were known. The bi- prefix comes from the observation that baking soda produces twice as much carbonate (CO3) per sodium as washing soda. So, HCO3– became bicarbonate, even though it only has one carbonate, and CO32- became carbonate.

The IUPAC Names

Baking soda is called sodium bicarbonate due to an outdated naming system, but the name is so familiar that it isn’t going anywhere. However, the International Union of Pure and Applied Chemistry (IUPAC) recommends the name sodium hydrogen carbonate for baking soda. If someone asks you to write the chemical formula for sodium hydrogen carbonate, you can get the right answer!

References

  • Ellingboe, J. L.; Runnels, J. H. (1966). “Solubilities of Sodium Carbonate and Sodium Bicarbonate in Acetone-Water and Methanol-Water Mixtures”. J. Chem. Eng. Data. 11 (3): 323–324. doi:10.1021/je60030a009
  • Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0.
  • Pradyot, Patnaik (2003). Handbook of Inorganic Chemicals. The McGraw-Hill Companies, Inc. p. 861. ISBN 978-0-07-049439-8.