medium importancemedium difficulty5 min

Sodium Hydroxide

Sodium hydroxide is a strong base, also called caustic soda, that dissolves in water to give a highly basic solution.

In one line: NaOH means strong base, strong caution.

Practice This Concept

Understand it

Sodium hydroxide is one of the most important laboratory and industrial chemicals in this chapter.
It is used in soap making, paper manufacture, and cleaning processes.
Because it is strongly basic, it must be handled carefully.
In water it produces hydroxide ions, which give its strong basic nature.

Example

A dilute sodium hydroxide solution turns red litmus blue and has a very high pH.

Rule to remember

NaOH dissolves in water to give Na⁺ and OH^- ions.

The OH^- ions are responsible for its strong basic nature.

See it worked out

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

Worked example

1If a student tests NaOH solution with red litmus, the litmus turns blue.
2That shows the solution is strongly basic and confirms sodium hydroxide as a base.

Method you can reuse

1First identify NaOH as sodium hydroxide.
2Then remember that it dissolves to give hydroxide ions.
3Finally connect those ions with strong basic behaviour and common uses.

Visual tip

A beaker sketch with NaOH pellets dissolving in water and a red litmus strip changing to blue is enough for revision.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

What type of substance is sodium hydroxide solution when it turns red litmus blue?

Think first, then show answer

It is a strong base because it gives a basic solution and changes red litmus to blue.

Common wrong answer

A common wrong answer is to call NaOH a salt because it contains sodium.

Why it loses marks: Its chemical behaviour is basic, not neutral.

Don't mix this up

Students sometimes treat sodium hydroxide as a salt because it has sodium in the name. It is actually a strong base.

Exam tip

If the question asks about NaOH, mention that it is a strong base and give one common use such as soap making.

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 often ask for the nature, use, or litmus behaviour of sodium hydroxide, or ask why it must be handled carefully.

1
Enough for 1 mark
Sodium hydroxide is a strong base, also called caustic soda, that dissolves in water to give a highly basic solution.
2
Add for 2 marks
Example: A dilute sodium hydroxide solution turns red litmus blue and has a very high pH.
3
Add for 3 marks
Sodium hydroxide is one of the most important laboratory and industrial chemicals in this chapter.

MCQ Quiz

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