NCERT Class VII Science Solutions: Chapter 5-Acids, Bases and Salts Part 5

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Question 22:

A farmer was unhappy because of his low crop yield. He discussed the problem with an agricultural scientist and realized that the soil of his field was either too acidic or too basic. What remedy would you suggest the farmer to neutralize the soil?

Answer:

If the soil is too acidic, it is treated with bases such as quick lime (calcium oxide) or slaked lime (calcium hydroxide), which neutralizes the excess acid present in the soil and reduce its acidic.

If the soil is too basic, organic matter is added to it. Organic matter releases acids which neutralizes the basic nature of the soil.

Question 23:

You are provided with four test tubes containing sugar solution, baking soda solution, tamarind solution, salt solution. Write down an activity to find the nature (acidic/basic/neutral) of each solution.

Answer:

Image of four taste tube with diffrent solution.

Image of Four Taste Tube with Diffrent Solution.

Image of four taste tube with diffrent solution.

We can use both red and blue litmus solutions to find the nature of each solution. In acidic media, blue litmus solution turns to red and in basic media, red litmus solution turns to blue.

Litmus Test of Common Items
Litmus test of common items

Solution

Effect on red litmus solution

Effect on blue litmus solution

Nature of solution found

Sugar Solution

No change

No change

Neutral

Baking soda solution

Red changes to blue colour

No change

Basic

Tamarind solution

No change

Blue changes to red colour

Acidic

Salt solution

No change

No change

Neutral

Question 24:

You are provided with three test tubes A, B and C as shown in Figure with different liquids. What will you observe when you put

  1. A piece of blue litmus paper in each test tube.

  2. A piece of red litmus paper in each test tube.

  3. A few drops of phenolphthalein solution to each test tube.

As showing in images is a observation in test tube

Observation in Test Tube

As showing in images is a observation in test tube

Answer:

Effect on and Effect on and Effect on Phenolphthalein Solution
Effect on and Effect on and Effect on phenolphthalein solution

Test Tube

Effect on

blue litmus

Effect on

red litmus

Effect on

phenolphthalein

solution

A.

Turns red

Remains red

Colourless

B.

Remains blue

Turns blue

Pink colour

C.

Remains blue

Remains red

Colourless

Question 25:

Paheli observed that most of the fish in the pond of her village were gradually dying. She also observed that the waste of a factory in their village is flowing into the pond which probably caused the fish to die.

  1. Explain why the fish were dying.

  2. If the factory waste is acidic in nature, how can it be neutralized?

Answer:

  1. Since factory waste may contain acids or bases, it can kill the fish.

  2. If the factory waste is acidic in nature, it can be neutralized by adding basic substances.

Question 26:

Explain two neutralization reactions related to daily life situation.

Answer:

  1. Indigestion: Our stomach contains hydrochloric acid. It helps us to digest food but too much of acid in the stomach causes indigestion. Sometimes, indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia which contains magnesium hydroxide. It neutralize hydroxide. It neutralize the effect of excessive acid.

  2. Ant sting: When an ant bite injects the acidic liquid into the skin, the effect of the acid can be neutralized by rubbing moist baking soda or calamine solution, which contains zinc carbonate.