Question

Which of the following is not an amphoteric substance?
(A) $HN{O_3}$
(B) $HCO_3^ - $
(C) ${H_2}O$
(D) $N{H_3}$

Answer 1

Hint: An amphoteric compound is a molecule or ion that can react both as an acid and as a base. Many metals like Copper, Zinc, Tin, Lead, Aluminum and Beryllium form amphoteric oxides and hydroxides.

Complete step by step answer:
(A) $HN{O_3}$ is also known as nitric acid and it donates ${H^ + }$ ions as well. Thus, $HN{O_3}$ is acidic in nature.
(B) $HCO_3^ - $ can both donate as well as accept the ${H^ + }$ ion. Thus, it is an amphoteric substance.
(C) ${H_2}O$ is also an amphoteric substance because when an acid donates the ${H^ + }$ ion, then the water acts as a Proton acceptor and hence acct as a base whereas, on the other hand, when a base reacts with water, the water molecule donates a proton and thus itself act as an acid.
(D) $N{H_3}$ does contain the hydrogen atoms that can be donated as ${H^ + }$ ions and do act as an acid. Also, due to the presence of lone pairs in $N{H_3}$, it is also capable of accepting the ${H^ + }$ ion and thus behave as a base. Thus, $N{H_3}$ is also amphoteric in nature.

Hence, the answer is option (A).

Note: The Amphoteric Substances do act as an electron acceptor or proton donor when reacted with a base while it does behave as a proton acceptor or electron donor when reacted with an acidic compound. Water ${H_2}O$ is the most common amphoteric substance.