NCERT Class 7 Science Chapter 2 Exploring Substances: Acidic, Basic, and Neutral Solutions to each chapter is provided in the list so that you can easily browse through different chapters NCERT Class 7 Science Chapter 2 Exploring Substances: Acidic, Basic, and Neutral and select need one. NCERT Class 7 Science Chapter 2 Exploring Substances: Acidic, Basic, and Neutral Question Answers Download PDF. NCERT Class 7 Science Solutions.
NCERT Class 7 Science Chapter 2 Exploring Substances: Acidic, Basic, and Neutral
Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. CBSE Class 7 Science Solutions are part of All Subject Solutions. Here we have given NCERT Class 7 Science Solutions and Textbook for All Chapters, You can practice these here.
Exploring Substances: Acidic, Basic, and Neutral
Chapter: 2
Page No – 9
Table 2.1: Testing the nature of samples with blue and red litmus papers.
| S.No. | Name of the sample | Colour of blue litmus paper after putting a drop of sample | Colour of red litmus paper after putting a drop of sample |
| 1. | Lemon juice | ||
| 2. | Soap solution | ||
| 3. | Amla juice | ||
| 4. | Tamarind water | ||
| 5. | Vinegar | ||
| 6. | Baking soda solution | ||
| 7. | Lime water | ||
| 8. | Tap water | ||
| 9. | Washing powder solution | ||
| 10. | Sugar solution | ||
| 11. | Salt solution | ||
| 12. | Any other |
Ans:
| S.No. | Name of the sample | Colour of blue litmus paper after putting a drop of sample | Colour of red litmus paper after putting a drop of sample |
| 1. | Lemon juice | Turns red | No change |
| 2. | Soap solution | No change | Turns blue |
| 3. | Amla juice | Turns red | No change |
| 4. | Tamarind water | Turns red | No change |
| 5. | Vinegar | Turns red | No change |
| 6. | Baking soda solution | No change | Turns blue |
| 7. | Lime water | No change | Turns blue |
| 8. | Tap water | No change | No change |
| 9. | Washing powder solution | No change | Turns blue |
| 10. | Sugar solution | No change | No change |
| 11. | Salt solution | No change | No change |
| 12. | Any other | Turns red | No change |
Page No : 13
Table 2.3: Testing the nature of samples with the red rose extract.
| S.No. | Name of the sample | The colour of the red rose extract after adding the sample | Nature of the substance |
| 1. | Lemon juice | ||
| 2. | Soap solution | ||
| 3. | Amla juice | ||
| 4. | ….. |
Ans:
| S.No. | Name of the sample | The colour of the red rose extract after adding the sample | Nature of the substance |
| 1. | Lemon juice | darker red or slightly pinkish. | Acidic. |
| 2. | Soap solution | Greenish or faded colour . | Basic. |
| 3. | Amla juice | Dark pink or red | Acidic. |
| 4. | Baking soda solution | Greenish | Basic. |
Page No – 15
Table 2.4: Testing the nature of samples with turmeric paper
| S.No | Name of the sample | The colour of the turmeric paper after putting a drop of the sample |
| 1 | Lemon juice | |
| 2 | Soap solution | |
| 3 | Amla juice | |
| 4 | ….. |
Ans:
| S.No | Name of the sample | The colour of the turmeric paper after putting a drop of the sample |
| 1 | Lemon juice | No change |
| 2 | Soap solution | Turned reddish – brown |
| 3 | Amla juice | No Change |
| 4 | Baking soda | Turned reddish – brown |
| 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?
(i) Lime water.
(ii) Baking soda.
(iii) Vinegar.
(iv) Common salt solution.
Ans: (iii) Vinegar.
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.
Ans: (iv) Basic, basic, and basic
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.
Ans: Fig. 2.13: Acidic (Red rose extract turns red in acid).
Fig. 2.14: Basic (Red rose extract turns green in base).
Fig. 2.15: Neutral (Red rose extract color is unchanged in neutral solutions).
4. A liquid sample from the laboratory was tested using various indicators:
| Indicator | Red litmus | Blue litmus | Turmeric |
| Change | No change | Turned red | No change in colour |
Based on the tests, identify the acidic or basic nature of the liquid and justify your answer.
Ans: The liquid is acidic.It turned Blue litmus turning red indicates the presence of an acid. Red litmus showing no change and turmeric showing no change further confirm that the solution is acidic.
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?
Ans: 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.
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.
Ans: Various materials that could be used for writing a message on a white sheet of paper, along with possible substances that could be in the spray bottle and the resulting color of the writing.
| Material for Writing | Substance in the Spray Bottle | Color of Writing |
| Lemon juice | Heat (iron, sunlight) | becomes brown when heated |
| Vinegar | Red Rose Extract | Red |
| Baking soda paste | Turmeric Solution | Red/Brown |
| Soap Solution | Turmeric Solution | Red/Brown |
| Lime Water | Turmeric Solution | Red |
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.
Ans: If baking soda is added to the mixture of grape juice and red rose extract, the color of the mixture will likely change. This happens because baking soda is a basic substance, and the pH change will affect the anthocyanin pigments present in both the grape juice and the red rose extract.When baking soda is added to this mixture, the red color is likely to turn purple or blue.
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?
Ans: Keerthi wrote a secret message to her grandmother on her birthday using orange juice, which is acidic due to the presence of citric acid. To reveal the hidden message, an indicator that changes color in acidic conditions can be used. Blue litmus solution would be a suitable choice, as it turns red in the presence of an acid. Alternatively, red rose extract can also be used, as it will turn red when exposed to an acidic substance like orange juice.
9. How can natural indicators be prepared? Explain by giving an example.
Ans: Natural indicators can be prepared using plant-based substances that change color in response to pH variations.
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.
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.
Ans: Yes, you can identify vinegar, baking soda solution, and sugar solution using only turmeric paper due to the distinct way each liquid interacts with this natural indicator. Turmeric paper contains curcumin, a natural pigment that turns reddish-brown in basic solutions and remains yellow in acidic or neutral solutions. To identify the liquids, you would take a small piece of turmeric paper and test each liquid separately. When a drop of vinegar, which is an acidic solution (containing acetic acid), is placed on the turmeric paper, there will be no color change, and the paper will remain yellow. Similarly, when a drop of sugar solution, which is a neutral solution, is placed on the turmeric paper, there will also be no color change, and the paper will stay yellow. However, when a drop of the baking soda solution, which is a basic solution (containing sodium bicarbonate), is placed on the turmeric paper, the color of the paper will change from yellow to reddish-brown.
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?
Ans: Liquid X is basic, as indicated by the fact that the red rose extract turns green in basic solutions. Amla juice, being acidic, will neutralize the base when added. Adding excess amla juice will lower the pH of the solution, making it more acidic. In this resulting acidic solution, the red rose extract indicator will change color and turn red, indicating the shift to an acidic environment.
12. Observe and analyse the information given in the following flowchart. Complete the missing information.
Ans: (i) The soil can be acidic in nature.
(ii) The soil can be basic in nature.
(iii) The acidic soil can be treated with basic substances like quicklime (calcium oxide) or slaked lime (calcium hydroxide).
(iv) The basic soil can be treated with organic matter like compost or manure (which releases acids while decomposing).
(v) 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.
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