Animated Solution for Chemistry - Periodicity in Properties: Which one of the following is an amphoteric oxide?

Have you ever met someone who can perfectly adapt to any situation? In the world of chemistry, some compounds possess this exact trait. We call them amphoteric oxides.

The word "ampho" means both. An amphoteric oxide is a chemical chameleon. When it encounters an acid, it acts like a base. When it encounters a base, it flips its behavior and acts like an acid! In both scenarios, the end result is the formation of salt and water.

Let's look at the options provided in our problem. We need to find the one that exhibits this dual behavior.

First, we have ${\text{Na}}_2\text{O}$. Sodium is a highly electropositive alkali metal from Group 1. Metallic oxides are characteristically basic. Therefore, sodium oxide will only react with acids, not bases.

Next, we have ${\text{SO}}_2$ and ${\text{B}}_2{\text{O}}_3$. Sulfur and boron are non-metals. Non-metallic oxides are generally acidic in nature. They will happily react with bases, but they will ignore acids.

This leaves us with $\text{ZnO}$, zinc oxide. Let's put it to the test!

Imagine dropping some solid $\text{ZnO}$ into a beaker of strong hydrochloric acid ($\text{HCl}$).

Almost immediately, a reaction occurs:

In this reaction, the hydrochloric acid is neutralized. This means that $\text{ZnO}$ is stepping up to act as a base. It successfully forms zinc chloride (a salt) and water.

Now, for the ultimate proof. What happens if we take $\text{ZnO}$ and mix it with a strong base like sodium hydroxide ($\text{NaOH}$)?

If $\text{ZnO}$ were purely basic, nothing would happen. But surprisingly, it reacts again!

Here, $\text{ZnO}$ acts as an acid, neutralizing the strong base to form sodium zincate (${\text{Na}}_2{\text{ZnO}}_2$) and water.

Because zinc oxide successfully reacts with both acids and bases, it perfectly fits the definition of an amphoteric oxide.

Pro Tip: Zinc oxide isn't the only chemical chameleon. For your JEE and NEET exams, make sure to memorize other common amphoteric oxides like ${\text{Al}}_2{\text{O}}_3$, $\text{PbO}$, $\text{SnO}$, and $\text{BeO}$. Recognizing these instantly will save you precious time during the exam!