When Acids Meet Bases
Class 7 Science · Chapter 2: Exploring Substances: Acidic, Basic, and Neutral · NCERT Curiosity section 2.2
Learn
Ishaan puts a drop of lemon juice with some water in a test tube and adds a drop of blue litmus solution: it turns red (acidic). Then he adds lime water drop by drop, swirling each time.
At one point the colour changes from red to blue: the solution is no longer acidic. The lime water has neutralised the acid. Add another drop of lemon juice and it turns red again.
When an acid and a base are mixed in the right amounts, the result is neither acidic nor basic. This is a neutralisation reaction. It forms a salt and water, and heat is given out: the test tube feels slightly warm.
Acid + Base → Salt + Water + Heat
Here "salt" means a new substance formed in the reaction, not only table salt. Neutralisation explains many puzzles at home and in nature, as we see next.
Explore: the neutralisation experiment.
- Put the steps in order.
Remember
- An acid and a base neutralise each other.
- Neutralisation forms salt and water and gives out heat.
Quick check
What forms when an acid neutralises a base?
- salt and water, with heat
- only gas
- more acid
- nothing
Answer
salt and water, with heat. Acid + base → salt + water + heat.
Think about it
Grape juice mixed with red rose extract has a red tint. What happens if baking soda is added slowly?
One answer
The acid in grape juice is neutralised; the red tint fades and, with excess baking soda, the mixture turns green (basic).
Practice
Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.