Let Us Enhance Our Learning
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: A solution that turns red litmus paper to blue is basic in nature. To reverse this change, you must neutralise the base by adding an acidic substance. Among the given options, vinegar is an acidic substance.
<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-0307163004445488"
crossorigin="anonymous"></script>2. 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, meaning it is basic.
- Solution B turns turmeric red. The yellow colour of turmeric turns red in basic solutions.
- Solution C turns red rose extract green. Red rose extract gives a green colour in basic solutions.
3. Label the nature of solutions present in each of the containers (Figs. 2.13, 2.14, and 2.15).
- Answer: While the specific images cannot be visually analyzed, you can label the containers using the established rules for the red rose extract indicator:
- If the strip turns red, it is an acidic solution.
- If the strip turns green, it is a basic solution.
- If there is no colour change, the solution is neutral.
4. 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 turned blue litmus paper to red, which indicates it is acidic in nature. Acidic substances do not change the colour of red litmus paper , and the yellow colour of turmeric remains unchanged in acidic solutions.
<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-0307163004445488"
crossorigin="anonymous"></script>5. Which indicator should Manya use to test the solutions and why?
- Answer: Manya should use an olfactory indicator, such as chopped onion strips.
- Explanation: Because Manya is blindfolded and cannot see colour changes, an olfactory indicator is required as its odour changes depending on whether the medium is acidic or basic.
6. Could you suggest various materials which can be used for writing the message on the white sheet of paper and what could be in the spray bottle?
- Answer: One working combination is using a soap solution to write the invisible message, and using a turmeric solution as the spraying liquid. Soap is a basic substance , and when turmeric is sprayed over it, the basic writing turns red, making the message visible.
7. What will happen if baking soda is added to this mixture? Justify your answer.
- Answer: The mixture will eventually change its colour to green.
- Explanation: The initial red tint indicates that grape juice is acidic, as red rose extract gives a red colour in acidic solutions. Baking soda is a basic substance. When the basic baking soda is added, a neutralisation reaction occurs: $Acid + Base \rightarrow Salt + Water + Heat$. If enough baking soda is added to make the overall mixture basic, the red rose extract will turn green.
8. Can you assist her grandmother in revealing the message? Which indicator would you use to make it visible?
- Answer: You can use red rose extract as the indicator.
- Explanation: Orange juice contains acids (such as citric and ascorbic acid) and is acidic in nature. Applying red rose extract over the paper will cause it to turn red upon contact with the acidic juice, revealing the hidden message.
<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-0307163004445488"
crossorigin="anonymous"></script>9. How can natural indicators be prepared? Explain by giving an example.
- Answer: Natural indicators can be prepared by extracting coloured compounds from plants, fruits, or flowers.
- Example (Red Rose Indicator): Collect and wash fallen petals of red roses. Crush the petals and place them in a glass tumbler. Pour hot water over them until completely immersed. Wait 5-10 minutes until the water is coloured, and then filter it. The resulting filtrate is the natural indicator.
10. Can you identify them only using turmeric paper? Explain.
- Answer: You can only successfully identify the baking soda solution, but not the other two.
- Explanation: Turmeric paper turns red in basic solutions, so it will identify the basic baking soda solution. However, turmeric paper remains unchanged (yellow) in both acidic and neutral solutions. Therefore, it cannot differentiate between the acidic vinegar and the neutral sugar solution.
11. 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 in nature because red rose extract turns green in basic solutions. Amla juice is acidic. When excess amla juice is added, it will neutralise the basic Liquid X. Once the solution becomes highly acidic from the excess amla juice, the indicator will change its colour from green to red.
12. Complete the missing information (Flowchart: Garden with plants showing signs of poor health).
- 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 Hydrangea flowers (which naturally grow blue in acidic soil and pink/red in basic soil).
- The acidic soil can be treated with lime, which is a base.
- The basic soil can be treated with organic matter like manure and composted leaves.
Dive Deeper
Why did bubbles occur with vinegar but not with soap solution?
- Answer: Bubbles appear because a chemical reaction takes place between the vinegar—which is an acid —and the material of the eggshell or marble, releasing a gas. Soap solution, on the other hand, is a basic substance and does not react with these materials in the same way, resulting in no bubbles.
Let Us Enhance Our Learning
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: A solution that turns red litmus paper to blue is basic in nature. To reverse this change, you must neutralise the base by adding an acidic substance. Among the given options, vinegar is an acidic substance.
2. 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, meaning it is basic.
- Solution B turns turmeric red. The yellow colour of turmeric turns red in basic solutions.
- Solution C turns red rose extract green. Red rose extract gives a green colour in basic solutions.
<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-0307163004445488"
crossorigin="anonymous"></script>3. Label the nature of solutions present in each of the containers (Figs. 2.13, 2.14, and 2.15).
- Answer: While the specific images cannot be visually analyzed, you can label the containers using the established rules for the red rose extract indicator:
- If the strip turns red, it is an acidic solution.
- If the strip turns green, it is a basic solution.
- If there is no colour change, the solution is neutral.
4. 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 turned blue litmus paper to red, which indicates it is acidic in nature. Acidic substances do not change the colour of red litmus paper , and the yellow colour of turmeric remains unchanged in acidic solutions.
5. Which indicator should Manya use to test the solutions and why?
- Answer: Manya should use an olfactory indicator, such as chopped onion strips.
- Explanation: Because Manya is blindfolded and cannot see colour changes, an olfactory indicator is required as its odour changes depending on whether the medium is acidic or basic.
6. Could you suggest various materials which can be used for writing the message on the white sheet of paper and what could be in the spray bottle?
- Answer: One working combination is using a soap solution to write the invisible message, and using a turmeric solution as the spraying liquid. Soap is a basic substance , and when turmeric is sprayed over it, the basic writing turns red, making the message visible.
7. What will happen if baking soda is added to this mixture? Justify your answer.
- Answer: The mixture will eventually change its colour to green.
- Explanation: The initial red tint indicates that grape juice is acidic, as red rose extract gives a red colour in acidic solutions. Baking soda is a basic substance. When the basic baking soda is added, a neutralisation reaction occurs: $Acid + Base \rightarrow Salt + Water + Heat$. If enough baking soda is added to make the overall mixture basic, the red rose extract will turn green.
<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-0307163004445488"
crossorigin="anonymous"></script>8. Can you assist her grandmother in revealing the message? Which indicator would you use to make it visible?
- Answer: You can use red rose extract as the indicator.
- Explanation: Orange juice contains acids (such as citric and ascorbic acid) and is acidic in nature. Applying red rose extract over the paper will cause it to turn red upon contact with the acidic juice, revealing the hidden message.
9. How can natural indicators be prepared? Explain by giving an example.
- Answer: Natural indicators can be prepared by extracting coloured compounds from plants, fruits, or flowers.
- Example (Red Rose Indicator): Collect and wash fallen petals of red roses. Crush the petals and place them in a glass tumbler. Pour hot water over them until completely immersed. Wait 5-10 minutes until the water is coloured, and then filter it. The resulting filtrate is the natural indicator.
10. Can you identify them only using turmeric paper? Explain.
- Answer: You can only successfully identify the baking soda solution, but not the other two.
- Explanation: Turmeric paper turns red in basic solutions, so it will identify the basic baking soda solution. However, turmeric paper remains unchanged (yellow) in both acidic and neutral solutions. Therefore, it cannot differentiate between the acidic vinegar and the neutral sugar solution.
<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-0307163004445488"
crossorigin="anonymous"></script>11. 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 in nature because red rose extract turns green in basic solutions. Amla juice is acidic. When excess amla juice is added, it will neutralise the basic Liquid X. Once the solution becomes highly acidic from the excess amla juice, the indicator will change its colour from green to red.
12. Complete the missing information (Flowchart: Garden with plants showing signs of poor health).
- 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 Hydrangea flowers (which naturally grow blue in acidic soil and pink/red in basic soil).
- The acidic soil can be treated with lime, which is a base.
- The basic soil can be treated with organic matter like manure and composted leaves.
<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-0307163004445488"
crossorigin="anonymous"></script>Dive Deeper
Why did bubbles occur with vinegar but not with soap solution?
- Answer: Bubbles appear because a chemical reaction takes place between the vinegar—which is an acid —and the material of the eggshell or marble, releasing a gas. Soap solution, on the other hand, is a basic substance and does not react with these materials in the same way, resulting in no bubbles.
<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-0307163004445488"
crossorigin="anonymous"></script>