Sodium bicarbonate (IUPAC name: sodium hydrogen carbonate) is a chemical compound with the formula NaHCO3. It is a salt composed of sodium ions and bicarbonate ions. 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). Since 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.

The prefix "bi" in "bicarbonate" comes from an outdated naming system and is based on the observation that there is twice as much carbonate (CO3) per sodium in sodium bicarbonate (NaHCO3) and other bicarbonates as in sodium carbonate (Na2CO3) and other carbonates. The modern way of analyzing the situation based on the exact chemical composition (which was unknown when the name "sodium bicarbonate" was coined) says this the other way around: there is half as much sodium in NaHCO3 as in Na2CO3 (Na versus Na2).

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