Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula NaHCO3. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder. It has a slight alkaline taste resembling that of washing soda (sodium carbonate). It is a component of the mineral natron and is found dissolved in many mineral springs. The natural mineral form is known as nahcolite. It is also produced artificially.

Since it has long been known and is widely used, the salt has many related names such as baking soda, bread soda, cooking soda, bicarbonate of soda. Colloquially, its name is shortened to sodium bicarb or bicarb soda. The word saleratus, from Latin sal æratus meaning "aerated salt", was widely used in the 19th century for both sodium bicarbonate and potassium bicarbonate. The term has now fallen out of common usage.

Sodium bicarbonate is primarily used in cooking (baking) where it reacts with other components to release carbon dioxide, that helps dough "rise". The acidic compounds that induce this reaction include phosphates, cream of tartar, lemon juice, yogurt, buttermilk, cocoa, vinegar, etc. Hence, sodium bicarbonate can be substituted for baking powder provided sufficient acid reagent is also added to the recipe. Many forms of baking powder contain sodium bicarbonate combined with one or more acidic phosphates or cream of tartar.

Sodium bicarbonate is used as an antacid to treat acid indigestion and heartburn An aqueous solution is administered intravenously for cases of acidosis, or when there is insufficient sodium or bicarbonate ions in the blood. This compound has also been used as for patients who have had a ureterosigmoidostomy.

A paste from baking soda can be very effective when used in cleaning and scrubbing.

A classic experiment involves pouring/dumping/mixing vinegar and baking soda. Water is also a common ingredient.

The mixture foams up as a result of the carbon dioxide that is produced. This effect is often used to make a model of an erupting volcano. Also see chemical volcano.

Acetic acid (HC₂H₃O₂ (or C₂H₄O₂ in solution), from the vinegar) reacts with aqueous (NaHCO₃), forming sodium acetate (NaC₂H₃O₂) and (H₂CO₃). As also happens in the carbonic acid then dissociates into water and carbon dioxide (H₂O, and CO₂).

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