Exploring Substances: Acidic, Basic, and Neutral — NCERT Solutions

Given:

• Grape juice mixed with red rose extract gives a red tint.
• Baking soda solution is added to this mixture.

Step 1 — Identify the nature of grape juice:
The red rose extract turns red in an acidic solution. Since the mixture turned red, grape juice is acidic in nature.

Step 2 — Identify the nature of baking soda:
Baking soda (sodium bicarbonate) is a basic substance.

Step 3 — Predict what happens:
When baking soda (a base) is added to the acidic grape juice + red rose extract mixture:

• The base will neutralise the acid present in the grape juice.
• As the solution becomes basic, the red rose extract will change its colour from red to green.

Conclusion: On adding baking soda to the mixture, the colour of the mixture will change from red to green. This is because baking soda is basic, and red rose extract turns green in a basic solution. The acid in grape juice gets neutralised by the base (baking soda), making the solution basic, which causes the colour change.

Given: A secret message is written using orange juice (which is acidic in nature, as it contains citric acid).

Concept: To reveal a message written with an acidic substance, we need an indicator that shows a distinct colour change in acidic conditions.

Suggested Indicator: Red rose extract or turmeric solution.

How to reveal the message:

Method 1 — Using Red Rose Extract:

• Prepare red rose extract by crushing red rose petals in hot water and filtering.
• Lightly spray or brush the red rose extract over the paper where the message is written.
• The areas where orange juice (acidic) was applied will turn red/pink, making the message visible against the background.

Method 2 — Using Turmeric Paper:

• Prepare turmeric paper by dipping filter paper in turmeric paste and drying it.
• Write the message on turmeric paper using orange juice.
• Since orange juice is acidic and turmeric does not change colour in acidic medium, this method may not work well.

Best Choice: Red rose extract is the best indicator to use, as it gives a clear red/pink colour in acidic solutions, making the message written with orange juice clearly visible.

Conclusion: Keerthi's grandmother can reveal the message by applying red rose extract over the paper. The writing done with orange juice (acidic) will appear as a red/pink colour against the background.

Answer:

Natural Indicators: Natural indicators are substances obtained from plants (flowers, leaves, fruits, etc.) that change colour in the presence of acidic or basic solutions. They help us identify whether a substance is acidic, basic, or neutral.

Preparation of a Natural Indicator — Red Rose Extract:

Materials required: Red rose petals, mortar and pestle, hot water, glass tumbler, lid, filter paper, funnel.

Steps:

1. Collect fallen petals of red roses and wash them with water.
2. Crush the petals using a mortar and pestle.
3. Place the crushed petals in a glass tumbler.
4. Pour hot water into the tumbler so that the petals are completely immersed.
5. Cover the tumbler with a lid and wait for 5–10 minutes until the water becomes coloured.
6. Filter the coloured liquid. The filtrate (liquid after filtration) is the red rose extract, which is used as a natural acid-base indicator.

How it works:

• Red rose extract turns red/pink in acidic solutions.
• Red rose extract turns green in basic solutions.
• It shows no change in neutral solutions.

Other examples of natural indicators: Turmeric, purple cabbage, beetroot, red hibiscus (gudhal), Indian blackberry (jamun).

Conclusion: Natural indicators can be easily prepared from plant materials available around us and are effective in identifying the acidic, basic, or neutral nature of substances.

Given: Three liquids — vinegar (acidic), baking soda solution (basic), sugar solution (neutral).
Tool available: Turmeric paper only.

Properties of Turmeric Paper:

• Turmeric paper is yellow in colour.
• In basic solutions → turmeric paper turns red/reddish-brown.
• In acidic solutions → turmeric paper shows no change (remains yellow).
• In neutral solutions → turmeric paper shows no change (remains yellow).

Procedure:

1. Label the three liquids as X, Y, and Z.
2. Dip a strip of turmeric paper into each liquid one by one.
3. Observe the colour change.

Observations and Identification:

Limitation: Turmeric paper can identify the basic solution (baking soda) easily, but it cannot distinguish between vinegar (acidic) and sugar solution (neutral) because both show no colour change with turmeric paper.

Conclusion: Using turmeric paper alone, we can partially identify the three liquids. We can identify baking soda solution (it turns turmeric paper reddish-brown), but we cannot distinguish between vinegar and sugar solution, as turmeric paper does not change colour in either acidic or neutral solutions. To fully identify all three, an additional indicator (such as red litmus or red rose extract) would be needed.

Given:

• Red rose extract turns liquid X to green.
• Excess amla juice is added to liquid X.

Step 1 — Identify the nature of liquid X:

Concept: Red rose extract turns green in a basic solution.

Since red rose extract turns liquid X green, liquid X is basic in nature.

Step 2 — What happens when excess amla juice is added to liquid X?

Concept: Amla (Indian gooseberry) juice is acidic in nature (it contains ascorbic acid/citric acid). When an acid is added to a basic solution, neutralisation occurs.

• Initially, the amla juice (acid) will neutralise the base in liquid X.
• As excess amla juice is added, the solution will first become neutral and then turn acidic.
• As the solution becomes acidic, the red rose extract (already present) will change its colour from green to red/pink.

Conclusion:

• Nature of liquid X: Basic
• Effect of adding excess amla juice: The basic liquid X will be neutralised by the acid in amla juice. With excess amla juice, the solution will become acidic, and the colour of the red rose extract will change from green to red/pink.

Given: A garden with plants showing signs of poor health due to the nature of the soil.

Completed Flowchart:

The soil can be → Acidic in nature.

The soil can be → Basic in nature.

Which indicator can be used to test the nature of the soil?
→ Litmus paper (red and blue), turmeric paper, or red rose extract can be used as indicators to test the nature of the soil.

(Method: Mix a small amount of soil with water, filter it, and test the filtrate with the indicator.)

The acidic soil can be treated with → Lime (calcium hydroxide / slaked lime) or wood ash, which are basic substances. Adding a base to acidic soil neutralises the excess acid and makes the soil suitable for plant growth.

The basic soil can be treated with → Organic matter / compost, or acidic substances such as organic acids (e.g., from decaying leaves). Adding acidic organic matter neutralises the excess base in the soil.

Summary Table:

Conclusion: The health of plants depends on the pH (acidic/basic/neutral nature) of the soil. By testing the soil with a suitable indicator and treating it with the appropriate substance, the soil can be made suitable for healthy plant growth.