Polyatomic ion
The covalent bonding is inside HCO₃⁻.
Carbon, oxygen and hydrogen are covalently connected within the hydrogen carbonate ion. Sodium belongs to the ionic lattice as Na⁺.
Ionic solid · hydrogen carbonate salt
Sodium bicarbonate
NaHCO₃
Sodium bicarbonate is an ionic compound made from Na⁺ and HCO₃⁻ ions in a 1:1 ratio. The hydrogen carbonate ion can both accept and donate a proton, which gives bicarbonate chemistry its buffering and acid-reactive behaviour.
Everyday distinction: baking soda is sodium bicarbonate. Baking powder is a formulated mixture that contains bicarbonate plus acidic and other ingredients.
Essentials
NaHCO₃ is Na⁺ + HCO₃⁻, not one covalent six-atom molecule.
The formula unit balances one +1 sodium ion with one −1 hydrogen carbonate ion. Keeping the polyatomic ion intact prevents the common mistake of drawing a covalent Na–O bond as though the compound were molecular.
Detail
Hydrogen carbonate is amphiprotic.
HCO₃⁻ sits between carbonic acid and carbonate in a proton-transfer sequence. It can accept H⁺ to form H₂CO₃-related species or donate H⁺ to form CO₃²⁻, depending on the environment.
Buffer chemistry
Amphiprotic does not mean perfectly neutral.
Which direction dominates depends on pH, concentrations, dissolved CO₂ and the other acid–base partners present.
Understand
Adding acid to bicarbonate releases carbon dioxide.
A proton converts hydrogen carbonate toward carbonic-acid chemistry, and CO₂ plus H₂O are formed. Escape of gaseous CO₂ helps drive the visible fizzing.
Everyday chemistry
Gas formation is why bicarbonate can leaven dough.
In a formulation, an acid source reacts with bicarbonate to generate CO₂ bubbles. The complete food system is much more than pure NaHCO₃ alone.
Reference identifiers
Names and identifiers that pin down the chemical identity.
| Formula | NaHCO₃ |
|---|---|
| CAS Registry Number | 144-55-8 |
| PubChem CID | 516892 |
| Standard InChI | InChI=1S/CH2O3.Na/c2-1(3)4;/h(H2,2,3,4);/q;+1/p-1 |
| Canonical SMILES | C(=O)(O)[O-].[Na+] |
Advanced
Push past the first model without losing the simple picture.
Why is 'bicarbonate' still used if the systematic name is hydrogen carbonate?
Both names are widely encountered. Hydrogen carbonate makes the presence of one acidic hydrogen explicit and aligns directly with the formula HCO₃⁻.
Does sodium bicarbonate contain carbonic-acid molecules?
Not as discrete H₂CO₃ molecules in the solid formula unit. The anion is HCO₃⁻; carbonic acid appears in related protonation equilibria.
Why can bicarbonate act as both acid and base?
It has one removable proton but also carries negative charge and electron density capable of accepting a proton.
Constituent elements