NCERT Solutions for Class 7 Science Chapter 2 Exploring Substances: Acidic, Basic, and Neutral

Have you ever made a weird face after biting into a lemon because it was so sour? Or have you ever noticed how slick your hands feel when you wash them with soap? These feelings aren't just random; they tell us something important about the things we touch every day. Welcome to the fun world of acids, bases, and neutral substances! In this chapter, you'll become a young scientific detective and learn how to test things like curd, vinegar, baking soda, and soap to see if they are acidic, basic, or neutral. You will be using magical tools like litmus paper, turmeric, and even red cabbage juice that change color like chameleons to show you what things really are.

This Story also Contains

1. NCERT Solutions for Class 7 Science Chapter 2 (Exercise Questions with Answer)
2. Approach to Solve Questions of Class 7 Science Chapter 2 Exploring Substances: Acidic, Basic, and Neutral
3. Topics In NCERT Solutions for Chapter 2: Exploring Substances: Acidic, Basic, and Neutral
4. NCERT Solutions for Class 7 Science Chapter-Wise
5. NCERT Books and NCERT Syllabus

Chemistry will come to life in the most vivid and startling ways, from your kitchen shelf to your school lab. Get ready to explore, experiment, and find out how the world around you is full of hidden hints that you may find out about by learning about acids and bases. By using these explanations, students can develop a strong basic knowledge and prepare themselves properly for exams. NCERT Solutions can provide solutions for other classes as well in a very easy-to-understand way, which experts have prepared.

NCERT Solutions for Class 7 Science Chapter 2 (Exercise Questions with Answer)

Question 1: A solution turns the red litmus paper to blue. Excess addition
of which of the following solution would reverse the change?
(i) Lime water
(ii) Baking soda
(iii) Vinegar
(iv) Common salt solution

Answer:

A red litmus paper turns to blue in a basic solution. To reverse the change, an acidic solution will be required. Lime water and baking soda are basic solutions and will turn red litmus blue. Common salt is a salt, It wouldn't affect the color change of the litmus paper. Vinegar contains acetic acid, hence it will turn reverse the change, and will turn blue litmus red.

Question 2: You are provided with three unknown solutions labelled A, B, and C, but you do not know which of these are acidic, basic, or neutral. Upon adding a few drops of red litmus solution to solution A, it turns blue. When a few drops of turmeric solution are added to solution B, it turns red. Finally, after adding a few drops of red rose extract to solution C, it turns green.
Based on the observations, which of the following is the correct sequence for the nature of solutions A, B, and C?
(i) Acidic, acidic, and acidic
(ii) Neutral, basic, and basic
(iii) Basic, basic, and acidic
(iv) Basic, basic, and basic

Answer:

Solution A: The red litmus solution is turned to blue, that means solution A is acidic.

Solution B: Turmeric solutions turn red in basic solutions, so solution B is basic.

Solution C: Rose water extract is a natural pH indicator. It turns green in acidic solution. So, solution C is acidic.

So the correct sequence is acidic, basic, acidic.

Question 3: Observe and analyse Figs. 2.13, 2.14, and 2.15, in which red rose extract paper strips are used. Label the nature of solutions present in each of the containers.

Answer:

Rose water extract gives different colors in acidic and basic solutions.

So, the solution in Figure 2.13 is basic, as it turns the rose water color strip green. Solution in Figure 2.12 is neutral, as we see no change in the strip color. Solution in Figure 2.15 is acidic, as it turns the strip to bright red.

Question 4:

A liquid sample from the laboratory was tested using various indicators:

Based on the tests, identify the acidic or basic nature of the liquid and justify your answer.

Answer:

We know, that in presence of acidic solution, blue litmus turns red, and in presence of basic solution red litmus turns blue. Also, turmeric solution turns red in presence of basic solution, and no color change is observed in acidic and neutral solution. So from this we can deduce that, since the liquid sample gives no change in red litmus and turmeric, it is acidic in nature. This can be confirmed by the blue litmus turning to red. So the liquid sample is acidic in nature.

Question 5: Manya is blindfolded. She is given two unknown solutions to test and determine whether they are acidic or basic. Which indicator should Manya use to test the solutions and why?

Answer:

Manya could use an indicator like litmus paper, but since she is blindfolded she’ll use an olfactory indicator. One such indicator is onion. She can do the following steps to test the solutions:

1. Take some finely chopped onions in a container, along with some strips of clean cotton cloth or filter paper.

2. Tightly close the container and leave it overnight.

3. Take two of the cotton cloth or filter paper strips from the container and check their odor. Keep them on a clean surface and put a few drops of the solution on the filter paper strips.

4. Allow the drops to spread on the strips.

5. Check the odor again.

So, in an acidic solution, the Onion smell remains, and in a basic solution, the Onion smell disappears. And therefore she can determine whether the solution is acidic or basic.

Question 6: Could you suggest various materials that can be used for writing the message on the white sheet of paper (given at the beginning of the chapter) and what could be in the spray bottle? Make a table of various possible combinations and the color of the writing obtained.

Answer:

Question 7: Grape juice was mixed with red rose extract; the mixture got a tint of red color. What will happen if baking soda is added to this mixture? Justify your answer.

Answer: When grape juice is mixed with red rose extract (a natural pH indicator), the resulting mixture shows a red tint, indicating that grape juice is acidic. Now, if you add baking soda (a basic substance) to this mixture, the solution will neutralize the acid in the mixture, and the solution will become basic. Now, the color of rose water extract will change to green, indicating the basicity of the solution.

Question 8: Keerthi wrote a secret message to her grandmother on her birthday using orange juice. Can you assist her grandmother in revealing the message? Which indicator would you use to make it visible?

Answer:
Keerthi used orange juice to write a secret message, which means she used mild acid as invisible ink. This kind of writing dries clear and becomes visible only under certain conditions. To make it visible, Keerthi’s grandmother can do any of the following steps:

1. Gently heat the paper using a candle or bulb. The sugars in the orange juice will caramelize, turning brown, revealing the message.

Or

2. She can use red cabbage juice. Since orange juice is acidic and red cabbage juice is an indicator, it may turn the writing pink/red.

Question 9: How can natural indicators be prepared? Explain by giving an example.

Answer:

Natural indicators are substances obtained from plants that can show a color change when added to acidic or basic solutions. These indicators help us identify whether a substance is an acid or a base using simple color reactions. Let’s try making your indicators using red flowers.

• Collect some fallen petals of red roses available in your surroundings. It is advised not to pluck flowers. You may pick petals or flowers fallen on the ground.

• Take a fistful of the collected petals of red roses and wash them with water.

• Crush the petals using a mortar and pestle.

• Place them in a glass tumbler.

• Pour some hot water into the glass tumbler to ensure that the crushed flower petals are completely immersed.

• Caution— Perform this step under the supervision of an adult.

• Cover the glass tumbler with a lid. Wait for 5 – 10 minutes till the water becomes colored, and filter it.

• The filtrate (liquid after filtration) is the required flower extract to be used as an acid-base indicator.

Question 10: Three liquids are given to you. One is vinegar, another is a baking soda solution, and the third is a sugar solution. Can you identify them only using turmeric paper? Explain.

Answer:

Question 11: The extract of red rose turns the liquid X to green. What will the nature of liquid X be? What will happen when excess of amla juice is added to liquid X?

Answer:

The extract of red rose turns liquid X green, which indicates that liquid X is basic. The red rose extract acts as a natural indicator that shows red or pink in acidic solutions and green in basic ones. Since the color turned green, it confirms that the solution is a base. When an excess amount of amla juice is added to liquid X, the acidic amla juice neutralizes the base. As more acid is added, the solution becomes less basic and eventually turns acidic. Due to this change in pH, the color of the mixture will gradually change from green back to red or pink, showing that the solution has now become acidic.

Question 12: Observe and analyze the information given in the following flowchart. Complete the missing information.

Answer:

A garden with plants showing signs of poor health. There can be two possibilities for the poor health of plants. They can be:

• The soil can be acidic.

• The soil can be basic.

We can use an indicator to know the nature ofthe soil. Litmus paper (or red cabbage juice as an alternative natural indicator) can be used as an indicator. After using the indicator, we can fix the soil by adding acidic or basic substances as required. The acidic soil can be treated with slaked lime (calcium hydroxide). The basic soil can be treated with organic matter (like compost or manure).

Approach to Solve Questions of Class 7 Science Chapter 2 Exploring Substances: Acidic, Basic, and Neutral

• Learn the fundamentals of acids, bases, and neutral substances as well as their characteristics before attempting to answer questions from Class 7 Science Chapter 2: Exploring Substances: Acidic, Basic, and Neutral.

• Pay attention to how substances are identified using natural indicators such as litmus, red cabbage, china rose, and turmeric. Observe instances of common bases (such as baking soda and soap solution) and acids (such as vinegar and lemon juice).

• Learn how neutralization works and practice identifying substances based on changes in indicator color, particularly in practical applications like treating indigestion or soil.

• Read each question carefully, apply the proper scientific reasoning based on the nature and reaction of substances, and connect it to everyday observations.

Topics In NCERT Solutions for Chapter 2: Exploring Substances: Acidic, Basic, and Neutral

1. Exploring Substances: Acidic, Basic, and Neutral

• Litmus as an indicator
• Red rose as an indicator
• Turmeric as an indicator

2. What Happens When Acidic Substances Mix with Basic Substances?

3. Neutralisation in Daily Life

NCERT Solutions for Class 7 Science Chapter-Wise

The chapterwise solutions are given below:

NCERT Books and NCERT Syllabus

The NCERT books and syllabus links for class 7 are given below:

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