Question

How are Bronsted Lowry acid and bases defined?

Answer 1

Bronsted and Lowry discovered a theory about an acid and base, and according to this theory an acid is that specie which will donate proton in the aqueous solution and base is a specie which will accepts proton in the aqueous solution.

Complete answer:
As we know that Bronsted Lowry acid will have the ability to donate or loses proton (${{\text{H}}^{\text{ + }}}$) from itself and Bronsted Lowry base will have ability to accepts proton (${{\text{H}}^{\text{ + }}}$) from outside. Nature of Bronsted Lowry acid and base will be predicted from the following below given chemical reaction:
-Let we consider a chemical reaction between sulfuric acid (${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$) and water molecule (${{\text{H}}_{\text{2}}}{\text{O}}$) is shown as follow:
${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{O}} \rightleftharpoons {\text{HSO}}_{\text{4}}^{\text{ - }}{\text{ + }}{{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}$
Here, sulfuric acid donates its proton to the water molecule and behaves as a Bronsted Lowry acid and on the other water molecule accepts proton from sulfuric acid and behaves as Bronsted Lowry base in the aqueous medium.
-Another chemical reaction for example is shown as follow:
${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{ + N}}{{\text{H}}_3} \rightleftharpoons {\text{HSO}}_{\text{4}}^{\text{ - }}{\text{ + N}}{{\text{H}}_4}^{\text{ + }}$
Here also sulphuric acid behaves as a Bronsted Lowry acid and ammonia behaves as a Bronsted Lowry base.

Note:
Here some of you may think that the species which donates hydroxide ion (${\text{O}}{{\text{H}}^{\text{ - }}}$) is also a Bronsted Lowry base, but that concept is not correct. Because according to the Bronsted Lowry theory only species which accept protons are a Bronsted Lowry base. So don’t get confused in between the Arhenius theory and Bronsted & Lowry acid - base theory.