Question

What is a conjugate acid and base pair? Explain with examples.

Answer 1

Hint :In order to explain a conjugate acid and base pair, we should have the knowledge of Bronsted-Lowry acid base theory. Conjugate base is formed by donating a proton from acid while conjugate acid is formed by accepting a proton from base. Hence conjugate acid –base pairs differ only in hydrogen ions $ ({{H}^{+}}) $ .

Complete Step By Step Answer:
According to the Bronsted-Lowry acid base theory concept, acids are proton donors whereas bases are proton acceptors. In order to explain a conjugate acid and base pair. Let us consider the following reaction:
 $ CH_3COOH+H_2O\to CH_3CO{{O}^{-}}+H_3{{O}^{+}} $
In the above reaction, we can see that acetic acid $ (CH_3COOH) $ donates a proton and obtains acetate ion $ (CH_3CO{{O}^{-}}) $ as a product. The product which is obtained from acid by donating a proton is called conjugate base. Hence, acetate ion $ (CH_3CO{{O}^{-}}) $ is the conjugate base of acetic acid. Similarly, water $ (H_2O) $ accepts a proton and thus behaves like a base and obtains hydronium ion $ (H_3{{O}^{+}}) $ as a product. The product which is obtained from base by accepting a proton is called conjugate acid. Hence, hydronium ion $ (H_3{{O}^{+}}) $ is the conjugate acid of water (base).
Therefore, water $ (H_2O) $ and hydronium ions $ (H_3{{O}^{+}}) $ are examples of conjugate acid-base pairs.

Additional Information:
Acetic acid is a weak acid i.e. partially dissociates in water to give hydrogen ions. On the other hand, water is amphoteric i.e. acts as both acid and base.

Note :
It is important to note that Bronsted-Lowry acid base theory describes the conjugate acid-base pair concept. According to this theory, conjugate base is formed by donating a proton from acid while conjugate acid is formed by accepting a proton from base. For instance, water $ (H_2O) $ and hydronium ions $ (H_3{{O}^{+}}) $ are examples of conjugate acid-base pairs.