BRONSTED-LOWRY CONCEPT OF ACIDS AND BASES
In 1923 J.N Bronsted and T.M Lowry work independently and proposed acid and base definitions based on proton transfer.
ACID: Acids is a substance that can donate a proton (H+).
BASE: Base is a substance that can accept a proton (H+).
FOR EXAMPLE:
When HCl is dissolved in H2O, HCl acts as Bronsted-Lowery acid because it donates a proton to H2O and H2O acts as Bronsted-Lowry base because it accepts a proton from HCl. Following reaction occurs.
\[HCl\; +\; H_{2}O\; \rightleftharpoons \; H_{3}O^{+}\; + \;Cl^{-}\]
Ammonia is a gas at room temperature. When it is dissolved in water, the following reaction occurs.
\[:NH_{3}\; +\; H_{2}O\; \rightleftharpoons \; NH_{4}^{+}\; + \;OH^{-}\]
In this reaction, Ammonia is a base, and H2O acts as an acid.
NOTE:
- The Bronsted-Lowry concept is also applicable to the reactions that do not occur in an aqueous solution.
- A substance can work as acid or base only if another substance act as base or acid respectively.
- Bronsted-Lowery concept is not limited to aqueous solutions like the Arrhenius concept but it is also applicable to the gaseous phase.
- An Arrhenius acid is also Bronsted-Lowry acid and the same is true for bases.
- For a substance to be a Bronsted-Lowry acid it must have a proton so that it can donate it.
- Some species can act as either acids or bases, depending on what the other reactant is.
LIMITATIONS:
- Certain substances behave as acid though they cannot donate a proton. For example SO3. Similarly, CaO behaves as a base but it cannot accept a proton. These are limitations of the Bronsted-Lowry concept.
- BF3 cannot be explained by this concept.
Tags
Acid bases and salts