Bronsted-Lowry Acid
Definition and meaning of Bronsted-Lowry Acid in chemistry.
A Brønsted–Lowry acid is a substance that donates a proton (H⁺ ion) to another substance during a chemical reaction.
In more detail
Proposed independently by Johannes Brønsted and Thomas Lowry in 1923, this definition is broader than the Arrhenius definition because it does not require water or even a solution, proton transfer can occur in any solvent or in the gas phase. In every Brønsted–Lowry reaction, the acid must transfer its proton to a base (the proton acceptor), and after losing the proton, the acid becomes its conjugate base. This framework explains acid-base behavior for species like ammonium ion or acetic acid that don't fit neatly into the older Arrhenius model.
Key facts
| Proposed by | Johannes Brønsted and Thomas Lowry (1923) |
|---|---|
| General reaction | HA + B → A⁻ + HB⁺ |
| Field | General Chemistry |
| Key feature | No solvent (e.g., water) required, unlike the Arrhenius definition |
In HCl(aq) + H2O(l) → Cl⁻(aq) + H3O⁺(aq), HCl acts as the Brønsted–Lowry acid by donating a proton to water, forming hydronium ion and chloride ion, its conjugate base.
Frequently asked questions
How does a Brønsted–Lowry acid differ from an Arrhenius acid?
An Arrhenius acid must increase H3O+ concentration in aqueous solution, while a Brønsted–Lowry acid is defined simply by its ability to donate a proton, even in nonaqueous or gas-phase reactions such as HCl(g) + NH3(g) → NH4Cl(s).
Can a Brønsted–Lowry acid react without a base present?
No. Proton transfer requires a proton acceptor (a Brønsted–Lowry base); the acid cannot release H+ into a reaction unless another species is available to accept it.