Exploring Substances: Acidic, Basic, and Neutral
1. A solution turns the red litmus paper to blue. Excess addition of which of the following solution would reverse the change?
Answer: (iii) Vinegar
Explanation: The solution turns red litmus to.ConcurrentMode blue, so it is basic. Adding an acidic solution like vinegar will neutralize the basic solution and may turn blue litmus red, reversing the change.
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?
Answer: (iv) Basic, basic, and basic
Explanation:
- Solution A turns red litmus blue, indicating it is basic.
- Solution B turns turmeric red, which happens with basic substances.
- Solution C turns red rose extract green, which also indicates a basic nature.
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:
- Fig. 2.13: Acidic (red rose extract turns red)
- Fig. 2.14: Neutral (red rose extract shows no change)
- Fig. 2.15: Basic (red rose extract turns green)
- Explanation: Red rose extract turns red in acidic solutions, green in basic solutions, and shows no change in neutral solutions.
4. A liquid sample from the laboratory was tested using various indicators: Red litmus: No change, Blue litmus: Turned red, Turmeric: No change in colour.
Based on the tests, identify the acidic or basic nature of the liquid and justify your answer.
Answer: The liquid is acidic.
Explanation: The liquid turns blue litmus red, which indicates it is acidic. It does not change red litmus or turmeric, which is consistent with acidic substances, as turmeric only changes color (to red) with basic substances.
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 should use an olfactory indicator like onion strips.
Explanation: Since Manya is blindfolded and cannot see color changes, she can use onion strips, which change odor when mixed with acidic or basic substances, allowing her to identify the nature of the solutions by smell.
6. Could you suggest various materials which 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 colour of the writing obtained.
Answer:
| Material for Writing | Spray Bottle Content | Colour of Writing |
|---|---|---|
| Soap solution | Turmeric solution | Red |
| Baking soda solution | Turmeric solution | Red |
| Lemon juice | Red rose extract | Red |
| Vinegar | Red rose extract | Red |
| Explanation: Basic substances like soap or baking soda turn turmeric red, and acidic substances like lemon juice or vinegar turn red rose extract red, making the message visible. |
7. Grape juice was mixed with red rose extract; the mixture got a tint of red colour. What will happen if baking soda is added to this mixture? Justify your answer.
Answer: The mixture will turn green.
Explanation: Grape juice is acidic, so it turns red rose extract red. Adding baking soda (a base) will neutralize the acidity and make the solution basic, causing the red rose extract to turn green.
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: Use red rose extract to reveal the message.
Explanation: Orange juice is acidic and will turn red rose extract red, making the message visible as red writing on the paper.
9. How can natural indicators be prepared? Explain by giving an example.
Answer: Natural indicators can be prepared by extracting color-changing substances from plants.
Example: To prepare a red rose indicator, collect fallen red rose petals, crush them, soak them in hot water for 5-10 minutes, and filter the liquid. This red rose extract turns red in acidic solutions and green in basic solutions.
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: Yes, they can be identified using turmeric paper.
Explanation:
- Baking soda solution (basic) will turn turmeric paper red.
- Vinegar (acidic) and sugar solution (neutral) will not change the turmeric paper’s yellow color.
- To differentiate vinegar from sugar solution, taste or another indicator (like litmus) would be needed, but turmeric identifies the baking soda solution.
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:
- Liquid X is basic (red rose extract turns green in basic solutions).
- Adding excess amla juice (acidic) will neutralize the basic nature and turn the solution acidic, making the red rose extract turn red.
12. Observe and analyse the information given in the following flowchart. Complete the missing information.
Answer:
- 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 or red rose extract.
- The acidic soil can be treated with lime (calcium hydroxide).
- The basic soil can be treated with organic matter like manure or compost.
Explanation: Acidic soil is treated with a base like lime, and basic soil is treated with acidic organic matter to neutralize it.
thank you
very nice solutions. I want solutions for class 7th science all chapters.