Sodium bicarbonate (IUPAC name: sodium hydrogen carbonate), commonly known as baking soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation (Na+) and a bicarbonate anion (HCO3−). Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder.
It has a slightly salty, alkaline taste resembling that of washing soda (sodium carbonate). The natural mineral form is nahcolite.
It is a component of the mineral natron and is found dissolved in many mineral springs. Because it has long been known and is widely used, the salt has many related names such as baking soda, bread soda, cooking soda, and bicarbonate of soda. In colloquial usage, the names sodium bicarbonate and bicarbonate of soda are often truncated; forms such as sodium bicarb, bicarb soda, bicarbonate, and bicarb are common.
The word saleratus, from Latin sal æratus meaning “aerated salt”, was widely used in the 19th century for both sodium bicarbonate and potassium bicarbonate. It is known as one of the E number food additives E500.
The prefix bi in bicarbonate comes from an outdated naming system and is based on the observation that there is twice as much carbonate (CO3) per sodium in sodium bicarbonate (NaHCO3) as there is in sodium carbonate (Na2CO3).
The modern chemical formulas of these compounds express their precise chemical compositions (which were unknown when the names sodium carbonate and sodium bicarbonate were coined) and show the same ratio the other way around: there is half as much sodium percarbonate in NaHCO3 as in Na2CO3 (disodium carbonate).