Science 3 Marks Question

The red rose extract turns red in acidic solutions and green in basic solutions. In Fig. (I), the red rose extract paper strip turns green, indicating that the solution in this container is basic in nature. In Fig. (II), there is no change in the colour of the strip, which shows that the solution is neutral. However, in Fig. (III), the strip turns red, indicating that the solution is acidic in nature.

The soil can be Acidic in nature. → The acidic soil can be treated with bases like lime.
The soil can be Basic in nature. → The basic soil can be treated with organic matter (e.g., manure, compost).
Which indicator can be used to test the nature of the soil? → An acid-base indicator (like litmus used on a soil-water mixture, or a soil testing kit) can be used.

The reaction between an acid and a base is called neutralisation. In this reaction, a salt and water are formed, and heat is also released.
Acid + Base → Salt + Water + Heat Neutralisation in daily life:
The sting of an ant contains formic acid, which causes pain and irritation. When we apply moist baking soda (a base), it neutralises the acid and gives relief. When soil becomes too acidic, plants cannot grow well. Farmers add lime (calcium oxide), which is a base, to neutralise the acid in the soil. If the soil is too basic, they add organic matter (compost) to make it neutral. Wastes from factories are often acidic. If this acidic water is released into rivers or lakes, it can harm plants and animals. So, before releasing it, factories add basic substances to neutralise the acids.

(a) Colour Change in Red Cabbage Extract

substance	Colour Change in Red Cabbage	Nature of the Substance
1. Lemon Juice	Reddish	Acidic
2. Soap Solution	Greenish-Yellowish	Basic
3. Toothpaste	Greenish-Blueish	Basic
4. Vinegar	Reddish	Acidic
5. Black tea	Reddish	Acidic

(b) Classifying Substances as Acidic or Basic
Acidic Substances: Turn red cabbage extract reddish. Examples are lemon juice, vinegar, and black tea.
Basic Substances: Turn red cabbage extract greenish-yellowish. Examples are soap solution and toothpaste.

(b) Baking soda
(c) Amla juice
(c) Baking soda.

(b) Acidic
(b) It neutralises the acid
(d) All of these

Liquid X is basic (red rose extract turns green in basic solutions). Amla juice is acidic. Adding excess acidic amla juice will neutralize the base and make the solution acidic. In the resulting acidic solution, the red rose extract indicator will turn red.

You can identify the baking soda solution, but not distinguish between vinegar and sugar solution. Explanation: Turmeric paper turns red in basic solutions. It shows no color change in acidic or neutral solutions.
Vinegar is acidic, baking soda solution is basic, and sugar solution is neutral. Only the basic baking soda solution will turn the yellow turmeric paper red. The other two will cause no change.

Natural indicators can be prepared from parts of plants like flowers or vegetables. Example (Red Rose Extract): Collect fallen red rose petals, wash them, crush them, place them in a beaker and add hot water. Let it stand until the water gets colored, then filter the liquid. The colored filtrate is the indicator.

Use an indicator that changes color in acidic conditions, as orange juice is acidic (contains citric acid). Suitable indicators are Blue litmus solution (will turn red) or Red rose extract (will turn red). Apply the indicator solution to the paper.

The mixture will likely turn green.
Justification: Grape juice turning the red rose extract red indicates it’s acidic. Baking soda is basic. Adding a base (baking soda) neutralizes the acid. If enough baking soda is added to make the solution basic, the red rose extract indicator will turn green.

The effect uses an acid-base indicator reaction.

Writing Solution (Nature)	Spraying Liquid (Indicator)	Color Obtained
Soap Solution (Basic)	Turmeric Solution	Red
Lime Water (Basic)	Turmeric Solution	Red
Baking Soda Soln (Basic)	Turmeric Solution	Red
Soap Solution (Basic)	Red Rose Extract	Green
Lemon Juice (Acidic)	Red Rose Extract	Red
Vinegar (Acidic)	Red Rose Extract	Red
Lemon Juice (Acidic)	Blue Litmus Solution	Red

Manya should use an olfactory indicator, such as onion strips. Because she is blindfolded, she cannot rely on visual color changes. Olfactory indicators change their smell in acidic or basic media, which she can detect.