CID 516892
NaHCO3
Sodium bicarbonate
- Na 1
- H 1
- C 1
- O 3
- IUPAC name
- sodium hydrogen carbonate
- Molar mass
- 84.0060(62) g/mol
- Atoms
- 6
- SMILES
- C(=O)(O)[O-].[Na+]
- InChIKey
- UIIMBOGNXHQVGW-UHFFFAOYSA-M
- PubChem CID
- 516892
Cooks know it as baking soda or bicarbonate of soda; chemists write NaHCO3 and, following IUPAC (the International Union of Pure and Applied Chemistry), call it sodium hydrogen carbonate. It is a salt of two ions: the sodium cation, Na+, and the hydrogen carbonate anion, HCO3−, usually called bicarbonate. The powder is white, odourless and faintly bitter. Its molar mass, the mass of one mole of formula units (a sodium ion with a bicarbonate ion), is 84.006 g/mol.
It dissolves in water, 10.3 g in every 100 g at 25 °C, but not in ethanol. In solution the sodium ion leaves the pH unchanged, so the acid and base chemistry belongs to the anion. Bicarbonate can react as an acid or as a base. It gives off carbon dioxide when warmed, and even weak acids break it down.
Structure and bonding
The drawing shows six atoms in two separate pieces. A sodium ion, charge +1, stands apart with no bond drawn to it. Beside it is the bicarbonate ion: a carbon atom joined to three oxygen atoms, one by a double bond and two by single bonds. A hydrogen atom sits on one singly bonded oxygen, and the −1 charge is drawn on the other.
That placement is one way of drawing the ion. In the related carbonate ion, OpenStax notes, the double bond could sit on any of the three oxygens. Carbonate is the average of those three resonance forms, with three identical C–O bonds. The drawing is also only one formula unit of a lattice. In the solid, each ion is pulled equally by all its oppositely charged neighbours, so the ions lock into a three-dimensional lattice.
The crystals are white monoclinic prisms. Like other ionic solids they conduct electricity poorly: the ions are held too strongly to move until the crystal dissolves. Calcium and magnesium hydrogen carbonates exist only in solution and turn into carbonates when the water evaporates. Sodium bicarbonate, by contrast, can be evaporated out of solution as a solid.
Where it turns up
Baking powder is baking soda premixed with a dry acid, for example potassium hydrogen tartrate, better known as cream of tartar. Beyond the kitchen, the uses PubChem gathers include antacids, mouthwashes, pharmaceuticals, veterinary medicine, soaps, detergents and animal feed. Fire extinguishers, artificial mineral water, sponge rubber and gold and platinum plating appear on the same lists.
One consumer-product database lists 429 products that contain it, from pet care to home maintenance. A separate product listing names carpet and cat-litter deodorisers among them. Cosmetics lists give it four jobs: buffer, abrasive, deodorant and oral-care ingredient. International food regulators class it as an acidity regulator and a raising agent.
It also works outdoors. The United States first registered it as a fungicide in 1994, and it is exempt from residue limits when applied as a fungicide to crops or to harvested produce.
Why it matters
Hydrogen carbonates are amphoteric: they act as weak acids and as weak bases. With hydroxide ions, bicarbonate gives up its proton and becomes carbonate and water. With an acid it goes the other way, forming a salt, carbon dioxide and water. That second reaction is how the salt serves as a source of carbon dioxide.
Heat breaks the solid down as well. PubChem’s data put the start above 50 °C, as carbon dioxide and water leave and sodium carbonate stays behind, with decomposition complete at 270 °C. The International Chemical Safety Card counts sodium oxides among the products. Dissolved, the salt begins to break up at about 20 °C and does so completely on boiling.
Industry makes most of it by passing carbon dioxide into saturated sodium carbonate solution; the less soluble bicarbonate crystallises out. Some is purified from crude Solvay-process bicarbonate. United States output in 2023 lay between 700 million and 850 million pounds, on Environmental Protection Agency figures. One breakdown puts food preparation first at 34 per cent, then animal feed at 24 per cent.
Properties
| Property | Value | Unit | Source |
|---|---|---|---|
| Formula (Hill order) | CHNaO3 | ||
| Molar mass | 84.0060(62) g/mol | g/mol | IUPAC/CIAAW 2024 |
| Sodium atoms | 1 | ||
| Hydrogen atoms | 1 | ||
| Carbon atoms | 1 | ||
| Oxygen atoms | 3 | ||
| PubChem molecular weight | 84.007 g/mol | g/mol | PubChem |
Safety
In its everyday forms, a baking ingredient or a tin of powder, sodium bicarbonate is essentially harmless. Of 6,838 company reports to the European Chemicals Agency, 99.4% find no hazard under the Globally Harmonized System (GHS); US food regulators affirm it as generally recognised as safe. The powder is mildly irritating to the eyes. The PubChem Laboratory Chemical Safety Summary is the authoritative sheet.
Questions
Is baking soda the same as sodium bicarbonate?
Yes. Baking soda, bicarbonate of soda and sodium bicarbonate are three everyday names for one compound, which IUPAC calls sodium hydrogen carbonate, NaHCO3. Baking powder is a different product: baking soda already mixed with a solid acid, such as cream of tartar, so that the acid needed to release carbon dioxide is in the same tin.
Why does baking soda make cakes rise?
Rising needs a gas trapped in the dough, and hydrogen carbonate ions supply carbon dioxide. In baking powder the soda sits beside a solid acid; while the powder stays dry nothing happens, but once water is added the acid reacts with the HCO3− ions and releases the gas. Dough holds the bubbles and expands in the oven.
Is sodium bicarbonate a molecule?
No. The drawing shows six atoms, but they belong to two separate ions, Na+ and HCO3−, with no bond joining them. That pair is one formula unit of an ionic lattice. In the crystal each ion is drawn equally to every oppositely charged neighbour, so no single sodium belongs to any single bicarbonate. The bonds drawn inside the bicarbonate ion join particular atoms; the ionic bonding between the ions is spread over all neighbours instead.
Why is a baking soda solution basic?
The sodium ion has no effect on pH, so everything depends on the bicarbonate ion, which is amphiprotic: it can give away a proton or accept one. Its base constant, Kb = 2.3 × 10−8, is far larger than its acid constant, Ka = 4.7 × 10−11, so accepting wins. A freshly made 0.1 molar solution measures pH 8.3 at 25 °C.
Made of the same elements
- CH3COONa Sodium acetate 8 atoms in one formula unit of an ionic lattice.
Appears in these articles
- An acid gives a proton and a base takes it: Arrhenius, Brønsted–Lowry and Lewis Hydrogen chloride gives its proton to water effectively completely; acetic acid gives only a small fraction.
Sources
- PubChem CID 516892, sodium bicarbonate
- IUPAC/CIAAW, Abridged Standard Atomic Weights 2024
- PubChem Laboratory Chemical Safety Summary for sodium bicarbonate (CID 516892)
- OpenStax, Chemistry 2e, §18.6 Occurrence, Preparation, and Properties of Carbonates
- OpenStax, Chemistry 2e, §14.4 Hydrolysis of Salts
- OpenStax, Chemistry 2e, §7.1 Ionic Bonding
- OpenStax, Chemistry 2e, §7.4 Formal Charges and Resonance