Question

What are the acid bases pairs in the following equation :
\[HCOOH(aq) + {H_2}O(l) \rightleftharpoons HCO{O^ - }(aq) + {H_3}{O^ + }(aq)\]?

Answer 1

Hint: According to Arrhenius concept strong acids and bases are as they are completely able to dissociate and produce \[{H_3}{O^ + }\] and \[O{H^{ - 1}}\] ions respectively in the medium. Alternatively according to Bronsted \[ - \] Lowry concept of acid and bases, where in a strong acid means a good proton donor.

Complete answer:
The word has been derived from a latin word meaning sour. Acids turn blue litmus paper into red and liberates di hydrogen on reacting with active metals. Similarly, bases are known to turn red litmus paper into blue. We know there are three concepts to understand what acid and bases are. These concepts are given by Arrhenius,the Bronsted \[ - \] Lowry and Lewis concepts.
We will be considering the concept of Bronsted \[ - \] Lowry Acids and bases.
According to it \[ - \] an acid is a substance which has a tendency to donate protons and base in a substance which has a tendency to accept protons.
From the given equation, \[HCOOH\] is an acid because it donates a \[{H^ + }\].
\[{\text{Acid}}\xrightarrow{{ - {H^ + }}}{\text{conjugate base}}\]
\[HCOOH\xrightarrow{{ - {H^ + }}}HCO{O^ - }\]
These acid base pairs are known as conjugate pairs. Similarly, \[{\text{base}}\xrightarrow{{ + {H^ + }}}{\text{conjugate acid}}\]
  \[{H_2}O\xrightarrow{{ + {H^ + }}}{H_3}{O^ + }\]. In the above reaction the same species of water can act as acid as well as base. Such species are called Amphiprotic species.

Note:
There were certain limitation of this concepts.It fails to explain the following \[ - \]
\[ \bullet \] Substance like \[AlC{l_3},B{F_{3,}},SnC{l_2}etc.\] behave as acids although they do not contain any hydrogen and hence, cannot give a proton.
\[ \bullet \] Acid oxides such as anhydrous \[C{O_{2,}}S{O_{2,}}S{O_3},etc.\] can neutralise basic oxides like \[CaO\] and \[BaO\], even in the absence of a solvent.
\[ \bullet \] Both Arrhenius and Bronsted \[ - \] Lowry concepts are limited to the substances which contain hydrogen and hence, cannot give a proton.