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Question: The conjugate base of \[HP{O_4}^{2 - }\] is A. \(P{O_4}^{3 - }\) B. \({H_2}P{O^ - }_4\) C. \({...

The conjugate base of HPO42−HP{O_4}^{2 - } is
A. PO43−P{O_4}^{3 - }
B. H2PO−4{H_2}P{O^ - }_4
C. H3PO4{H_3}P{O_4}
D. H3PO3{H_3}P{O_3}

Explanation

Solution

Hint: The strength of an acid and its conjugate base are inversely related. We can define conjugate base as a substance formed when an acid loses a hydrogen ion. The substance is base as it donates a hydrogen ion from acid. According to Bronsted Lowry theory of acids and bases, an acid is a proton donor and base is a proton acceptor. The general reaction between a conjugate acid and conjugate base is as follows; HX+H2O→X−+H3O+HX + {H_2}O \to {X^ - } + {H_3}{O^ + }. Conjugate can be easily recognised in an acid-base reaction as it is an anion.

Complete answer:
In the given problem the conjugate base of HPO42−HP{O_4}^{2 - }can be recognised with the help of its reaction with water which is : HPO42−+H2O→PO43−+H3O+HP{O_4}^{2 - } + {H_2}O \to P{O_4}^{3 - } + {H_3}{O^ + } hence in this reaction we observed that HPO42−HP{O_4}^{2 - } removes one hydrogen ion and gives PO43−P{O_4}^{3 - } which is conjugate base. The conjugate base of HPO42−HP{O_4}^{2 - } is PO43−P{O_4}^{3 - }.Thus option A is the correct answer to this problem. Some acids are capable of donating multiple protons hence the conjugate base of an acid can be acidic itself.

Note: We know that all acids have conjugate bases. In reaction, HX+H2O→X−+H3O+HX + {H_2}O \to {X^ - } + {H_3}{O^ + } ;HXHX reacts with water molecules to create conjugate acid base pairs. Here X−{X^ - } is conjugate base. An acid donates a proton from its conjugate base while base can accept a proton from its conjugate acid. The conjugate acid and base pairs make a simple statement about relative statements about relative strength of acid and bases. On the other hand it has observed that a conjugate base is left over after acid donates a proton during chemical reaction.