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Non-Metal Oxides

Non-metal oxides are usually acidic oxides formed when non-metals combine with oxygen.

In one line: Non-metal oxide usually means acidic oxide.

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Understand it

Many non-metal oxides dissolve in water to form acids or react with bases to form salt and water. Carbon dioxide and sulphur dioxide are common examples. Their acidic nature is often tested through indicators and reaction pattern questions.

Example

Carbon dioxide is a non-metal oxide and shows acidic behaviour in water.

Rule to remember

Rule: non-metal oxides are usually acidic; they may form acids in water or react with bases to give salt and water.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

Carbon dioxide dissolves in water to form carbonic acid, which is why it is treated as an acidic oxide in school-level chemistry.

Method you can reuse

  1. 1Identify the oxide as a non-metal oxide.
  2. 2Check whether it forms acid in water or reacts with a base.
  3. 3If yes, call it acidic.
  4. 4Support the answer with one example.

Visual tip

A simple flow diagram showing non-metal + oxygen → acidic oxide → acid in water helps memory.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

A gas formed by burning carbon changes moist blue litmus red after dissolving in water. What does this show about the oxide?

Think first, then show answer
It shows the oxide is acidic, which is the usual behaviour of many non-metal oxides such as carbon dioxide.

Common wrong answer

Basic oxide is the common wrong answer because students sometimes apply the metal-oxide rule to non-metals too.

Don't mix this up

Students sometimes think every oxide is basic, but non-metal oxides are generally acidic.

Exam tip

If a non-metal oxide reacts with base or forms acid in water, think acidic oxide.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Questions may ask for the nature of carbon dioxide, sulphur dioxide, or the indicator change caused by a non-metal oxide.
  1. 1

    Enough for 1 mark

    Non-metal oxides are usually acidic oxides formed when non-metals combine with oxygen.

  2. 2

    Add for 2 marks

    Example: Carbon dioxide is a non-metal oxide and shows acidic behaviour in water.

  3. 3

    Add for 3 marks

    Many non-metal oxides dissolve in water to form acids or react with bases to form salt and water.

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