An amphoteric oxide is an oxide that can act as either an acid or base in a reaction to produce a salt and water. Amphoterism depends on the oxidation states available to a chemical species. Because metals have multiple oxidation states, they form amphoteric oxides and hydroxides.


Metals that display amphoterism include copper, zinc, lead, tin, beryllium, and aluminum.

Al2O3 is an amphoteric oxide. When reacted with HCl, it acts as a base to form the salt AlCl3. When reacted with NaOH, it acts as an acid to form NaAlO2.

Typically, oxides of medium electronegativity are amphoteric.

Amphiprotic Molecules

Amphiprotic molecules are a type of amphoteric species that donate or accept H+ or a proton. Examples of amphiprotic species include water (which is self-ionizable) as well as proteins and amino acids (which have carboxylic acid and amine groups).

For example, the hydrogen carbonate ion can act as an acid:

HCO3− + OH− → CO32− + H2O

or as a base:

HCO3− + H3O+ → H2CO3 + H2O

Keep in mind, while all amphiprotic species are amphoteric, not all amphoteric species are amphiprotic. An example is zinc oxide, ZnO, which does not contain a hydrogen atom and cannot donate a proton. The Zn atom can act as a Lewis acid to accept an electron pair from OH−.

**Amphoteric Oxide**

Amphoteric oxides are a specific type of chemical compound that can act as both an acid and a base. The term "amphoteric" comes from the Greek words "amphi" meaning "both" and "teros" meaning "ending". These oxides have the ability to react with both acids and bases, displaying characteristics of both acidic and basic behavior.

**Definition and Examples**

Amphoteric oxides are compounds composed of oxygen and at least one other element. They are capable of reacting with both acids and bases, exhibiting dual behavior. Some examples of amphoteric oxides include:

1. Aluminum Oxide (Al2O3): This oxide is amphoteric in nature and can react with both acids and bases. When it reacts with an acid, it behaves as a base and forms a salt. Conversely, when it reacts with a base, it acts as an acid and forms a salt.

2. Zinc Oxide (ZnO): Another common example of an amphoteric oxide is zinc oxide. It can react with both acids and bases, showing characteristics of both an acid and a base.

3. Lead Oxide (PbO): Lead oxide is also an amphoteric oxide that can react with both acids and bases.

**Acidic Behavior**

When an amphoteric oxide reacts with an acid, it acts as a base and undergoes a neutralization reaction. In this reaction, the oxide accepts a proton (H+) from the acid, resulting in the formation of a salt and water. The oxide acts as a base by donating a pair of electrons to the proton, forming a covalent bond.

**Basic Behavior**

On the other hand, when an amphoteric oxide reacts with a base, it acts as an acid. It donates a proton to the base, resulting in the formation of a salt and water. The oxide acts as an acid by accepting a pair of electrons from the base, forming a covalent bond.

**Conclusion**

Amphoteric oxides are unique compounds that exhibit both acidic and basic behavior. They can react with both acids and bases, forming salts and water. Some common examples of amphoteric oxides include aluminum oxide, zinc oxide, and lead oxide. Understanding the amphoteric nature of these compounds is important in various chemical reactions and applications.