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Amphoteric Oxide

An amphoteric oxide is an oxide that reacts with both acids and bases.

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Student-friendly explanation

Amphoteric oxides show a special nature because they can behave as acidic or basic oxides depending on the substance they react with. Zinc oxide and aluminium oxide are important examples. This property is often tested using reaction comparison questions.

How to write this in exams

  1. 1

    Start with the exact idea

    An amphoteric oxide is an oxide that reacts with both acids and bases.

  2. 2

    Then show how to use it

    1. Check whether the oxide reacts with acid. 2. Check whether it also reacts with base. 3. If both happen, write amphoteric. 4. Quote one example such as ZnO or Al2O3.

  3. 3

    Add one concrete example

    Zinc oxide reacts with both hydrochloric acid and sodium hydroxide.

  4. 4

    Avoid this incomplete answer

    Basic oxide is the common wrong answer because many students remember only the metal-oxide rule and forget exceptions.

Definition

An amphoteric oxide is an oxide that reacts with both acids and bases.

Example

Zinc oxide reacts with both hydrochloric acid and sodium hydroxide.

Rule to remember

Rule: amphoteric oxides react with acids as well as bases; common examples are ZnO and Al2O3.

Memory hook

Two-sided reaction means amphoteric nature.

Examples and method

Worked example

If zinc oxide reacts with dilute HCl to form zinc chloride and also reacts with NaOH to form sodium zincate, the oxide is amphoteric.

Method to apply

1. Check whether the oxide reacts with acid. 2. Check whether it also reacts with base. 3. If both happen, write amphoteric. 4. Quote one example such as ZnO or Al2O3.

Diagram support

A two-arrow comparison diagram showing one oxide reacting with acid and base is enough for quick revision.

How CBSE asks it

Exam questions may ask for the nature of zinc oxide or aluminium oxide, or ask why they are different from ordinary basic oxides.

Avoid common mistakes

Common confusion

Students often call every metal oxide basic, but some oxides like zinc oxide and aluminium oxide are amphoteric.

Common wrong answer

Basic oxide is the common wrong answer because many students remember only the metal-oxide rule and forget exceptions.

Exam tip

If an oxide reacts with both acid and base, amphoteric is the correct idea.

Quick check

A white oxide dissolves in both dilute hydrochloric acid and sodium hydroxide solution. What type of oxide is it?

It is amphoteric, because it reacts with both acids and bases.

Answer writing and exam use

1-mark answer

An amphoteric oxide is an oxide that reacts with both acids and bases.

2-mark answer

An amphoteric oxide is an oxide that reacts with both acids and bases. Rule: amphoteric oxides react with acids as well as bases; common examples are ZnO and Al2O3. Zinc oxide reacts with both hydrochloric acid and sodium hydroxide.

3-mark answer

Amphoteric oxides show a special nature because they can behave as acidic or basic oxides depending on the substance they react with. Zinc oxide and aluminium oxide are important examples. This property is often tested using reaction comparison questions. Rule: amphoteric oxides react with acids as well as bases; common examples are ZnO and Al2O3. If zinc oxide reacts with dilute HCl to form zinc chloride and also reacts with NaOH to form sodium zincate, the oxide is amphoteric. Exam questions may ask for the nature of zinc oxide or aluminium oxide, or ask why they are different from ordinary basic oxides. Basic oxide is the common wrong answer because many students remember only the metal-oxide rule and forget exceptions.
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