Question

In the following reaction, $HC{O_3}^ - $ is the conjugate acid of which base?
$HC{O_3}^ - + {H_2}O \to {H_3}{O^ + } + C{O_3}^{2 - }$
A.${H_3}{O^ + }$
B.${H_2}C{O_3}$
C.$C{O_3}^{2 - }$
D.${H_2}O$

Answer 1

Hint: Conjugate acid: Those acids which are formed by base after losing one hydroxide ion or accepting one hydrogen ion, are known as conjugate acid.
Conjugate base: Those bases which are formed by acids after losing one hydrogen ion, are known as conjugate base.

Complete step by step solution:
First of all we will discuss acids, bases and amphoteric compounds.
Acids: Those compounds which on ionization produce \[{H^ + }\]ions, are known as acids. They are sour in taste. Acids change the color of litmus from blue to red. When they react with bases then they become less acidic.
Bases: Those compounds which on ionization produce $O{H^ - }$ions, are known as bases. They are slippery in nature. Bases change the color of litmus from red to blue. When they react with acids then they become less basic.
Amphoteric Compounds: Those compounds which can react with both acids and bases are known as amphoteric compounds.
In the reaction we are given with the compounds as: ${H_3}{O^ + },{H_2}C{O_3},C{O_3}^{2 - }$ and ${H_2}O$. And we have to tell that $HC{O_3}^ - $ is the conjugate acid of which base?
Now let us first see what is conjugate acid and conjugate base.
Conjugate acid: Those acids which are formed by base after losing one hydroxide ion or accepting one hydrogen ion, are known as conjugate acid.
Conjugate base: Those bases which are formed by acids after losing one hydrogen ion, are known as conjugate base.
Here we are given with $HC{O_3}^ - $ as conjugate acid so the base will be $C{O_3}^{2 - }$ because when this base ($C{O_3}^{2 - }$) accepts one hydrogen ion it will converted into $HC{O_3}^ - $ which is known as conjugate acid of this base.

Hence option C is correct.

Note:
Hydrogen acts as an acid as well as base. When hydrogen accepts an acid then it converted into ${H_3}{O^ + }$ in this case water act as base and the ion i.e. hydronium ion formed will act as conjugate acid and similarly when water loss one hydrogen ion then it converted into $O{H^ - }$ and then water will act as acid and the ion formed i.e. hydroxide ion will act as its conjugate base.