2. Exploring Substances: Acidic, Basic, and Neutral

Answer: (iii) Vinegar

The solution is basic because it turns red litmus blue. Vinegar is acidic. Excess vinegar neutralises the base and makes the solution acidic. So the litmus turns red again.

Answer: (iv) Basic, basic, and basic

• A turns red litmus blue → basic.
• B turns turmeric red → basic.
• C turns red rose extract green → basic.

• Fig. 2.13: The strip turns green. The solution is basic.
• Fig. 2.14: The colour of the strip does not change. The solution is neutral.
• Fig. 2.15: The strip turns red. The solution is acidic.

The liquid is acidic.

• Blue litmus turns red only in an acidic solution.
• Red litmus does not change in an acidic solution.
• Turmeric does not change in an acidic solution. It turns red only in a basic solution.

Manya should use an olfactory indicator, such as onion strips (cloth strips kept with chopped onion).

Olfactory indicators change their smell in acidic or basic solutions. Manya cannot see a colour change, but she can smell the change. So an olfactory indicator is the right choice for her.

The red colour shows that grape juice is acidic. Baking soda is basic. On adding baking soda, the acid gets neutralised. So the red colour fades.

If excess baking soda is added, the mixture becomes basic and turns green.

Orange juice is acidic. The grandmother can spray blue litmus solution or red rose extract on the paper.

Both turn red with an acid. So the message will appear in red colour.

Natural indicators are made from flowers, fruits, vegetables or spices. Example — red rose extract:

1. Collect fallen petals of red roses and wash them with water.
2. Crush the petals using a mortar and pestle and place them in a glass tumbler.
3. Pour hot water to cover the petals (with the help of an adult). Cover the tumbler and wait for 5–10 minutes till the water becomes coloured.
4. Filter it. The filtrate is the red rose extract.

It turns red in acidic solutions and green in basic solutions. Turmeric paste, beetroot, purple cabbage and red hibiscus can also be used in the same way.

Yes.

1. Put a drop of each liquid on turmeric paper. The one that turns the paper red is the baking soda solution (basic).
2. Vinegar (acidic) and sugar solution (neutral) both show no change. To separate them, put a drop of each on the red spot made by baking soda.
3. The liquid that turns the red spot back to yellow is vinegar, because it neutralises the base. The one that causes no change is the sugar solution.

Liquid X is basic, because red rose extract turns green in a basic solution.

Amla juice is acidic. Excess amla juice will neutralise X and make it acidic. So the colour will change from green to red.

Eggshell and marble are made of calcium carbonate. Vinegar is acidic. It reacts with calcium carbonate and gives out carbon dioxide gas. This gas forms bubbles.

Soap solution is basic. It does not react with calcium carbonate. So no bubbles are seen.