๐ Class 7 Science Curiosity – Chapter 2 Solutions
๐งช Exploring Substances: Acidic, Basic and Neutral | Amresh Academy
๐ ๐น Question 1
1. A solution turns the red litmus paper to blue. Excess addition of which of the following solution would reverse the change?
๐ Answer: (iii) Vinegar ๐
๐ ๐น Question 2
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?
๐ Answer: (iv) Basic, basic and basic ⚡
๐ Explanation:
- A → Red litmus turns blue → Basic ๐งผ
- B → Turmeric turns red → Basic ๐ฅ
- C → Rose extract turns green → Basic ๐ข
๐ ๐น Question 3
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.
๐ Answer:
- Fig. 2.13 → Acidic ๐ด
- Fig. 2.14 → Basic ๐ข
- Fig. 2.15 → Neutral ⚪
๐ Explanation:
- Red rose extract turns red in acid
- Turns green in base
- Shows no change in neutral solution
๐ ๐น Question 4
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.
๐ Justification:
- It turns blue litmus red ๐ด, which confirms acidic nature
- No change in turmeric also supports this
๐ ๐น Question 5
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?
๐ Explanation:
- She cannot see color changes
- Olfactory indicators change smell, which she can detect ✔️
๐ ๐น Question 6
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.
๐ Answer:
Writing Solution ✍️ | Spraying Liquid ๐ง | Colour ๐จ |
Soap solution (Basic) | Turmeric solution | Red ๐ด |
Lime water (Basic) | Turmeric solution | Red ๐ด |
Baking soda solution (Basic) | Turmeric solution | Red ๐ด |
Soap solution (Basic) | Red rose extract | Green ๐ข |
Lemon juice (Acidic) | Red rose extract | Red ๐ด |
Vinegar (Acidic) | Red rose extract | Red ๐ด |
Lemon juice (Acidic) | Blue litmus solution | Red ๐ด |
๐ ๐น Question 7
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.
๐ Explanation:
- Grape juice is acidic ๐ → turns rose extract red
- Baking soda is basic ๐งผ
- Adding base → neutralisation → then basic → turns green
๐ ๐น Question 8
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?
๐ Explanation:
- Orange juice is acidic ๐
- Indicators will change color → message becomes visible
๐ ๐น Question 9
9. How can natural indicators be prepared? Explain by giving an example.
๐ Example (Red Rose Extract ๐น):
- Collect petals
- Wash and crush them
- Add hot water
- Filter the solution
๐ This coloured solution acts as an indicator ✔️
๐ ๐น Question 10
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.
๐ Explanation:
- Baking soda → turns turmeric red ๐ฅ (basic)
- Vinegar → no change (acidic)
- Sugar → no change (neutral)
๐ ๐น Question 11
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?
๐ Answer:
- Liquid X is basic ๐ข
- Adding amla juice (acidic ๐) → solution becomes acidic
๐ Indicator will turn red ๐ด
๐ ๐น Question 12
12. Observe and analyse the information given in the following flowchart. Complete the missing information.
๐ Answer:
- Soil acidic → add lime ๐งช
- Soil basic → add organic matter ๐ฟ
- Indicator → litmus / soil test kit
✍️ ๐น Very Short Answer Type Questions
1. What surprising thing happened with Ashwin and Keerthi at the science fair?
๐ Answer:
✨ Their white sheets showed the message “Welcome to the Wonderful World of Science” after being sprayed with a liquid.
๐คฏ This made them curious and excited about science experiments.
2. What is litmus obtained from?
๐ Answer:
๐ฟ Litmus is obtained from lichens (a combination of fungus and algae).
๐ It is available as red and blue paper strips or solution.
3. What does a substance turning blue litmus paper red indicate?
๐ Answer:
๐ด It indicates that the substance is acidic in nature.
4. What does a basic substance feel like when touched?
๐ Answer:
๐งผ Basic substances feel slippery or soapy when touched (e.g., baking soda solution).
5. What is an olfactory indicator?
๐ Answer:
๐ Olfactory indicators are substances whose smell changes in acidic or basic conditions (e.g., onion).
๐ง ๐น Short Answer Type Questions
1. What do we learn by grouping samples into Group A, B, and C in the litmus test?
๐ Answer:
๐
- Group A → Acidic (blue litmus → red ๐ด)
- Group B → Basic (red litmus → blue ๐ต)
- Group C → Neutral (no change ⚪)
➡️ Helps in easy classification of substances
2. How does red rose extract work as an indicator?
๐ Answer:
๐น
- Acidic → turns red ๐ด
- Basic → turns green ๐ข
- Neutral → no change
➡️ It is a natural indicator
3. How is turmeric used as an indicator?
๐ Answer:
๐ผ Turmeric paper:
- Basic → turns red ๐ด
- Acidic/Neutral → remains yellow ๐ก
4. What happens in a neutralisation reaction?
๐ Answer:
⚖️ Acid + Base → Salt + Water + Heat
๐ฅ This reaction releases heat and forms a neutral solution
5. Why did moist baking soda help Ashwin after an ant bite?
๐ Answer:
๐ Ant injects formic acid
๐งช Baking soda (base) neutralises it
➡️ Pain gets relieved ๐
๐ ๐น Descriptive Answer Type Questions
1. Explain how soil treatment helps plants grow better.
๐ Answer:
๐ฑ
- Acidic soil → add lime (base)
- Basic soil → add organic matter (compost)
➡️ Maintains soil pH balance for healthy plant growth
2. How does neutralisation help in industrial waste treatment?
๐ Answer:
๐ญ Acidic waste harms aquatic life ๐
➡️ Adding base neutralises it
๐ Protects environment and water life
3. Why can’t turmeric be used to test acidic substances?
๐ Answer:
๐ผ Turmeric shows change only in basic solutions
❌ No change in acid or neutral
➡️ Cannot detect acidity
4. What does the hydrangea flower’s colour tell about soil?
๐ Answer:
๐ธ
- Acidic soil → Blue flowers ๐ต
- Basic soil → Pink/Red flowers ๐ด
➡️ Indicates soil nature
5. Why should we not taste unknown substances during experiments?
๐ Answer:
⚠️ Unknown substances may be poisonous or harmful
➡️ Always follow safety rules in lab ๐งช
๐ ๐น Exploring Type Questions
1. How could Ashwin’s “secret greeting card” trick work?
๐ Answer:
๐จ Paper coated with turmeric
✍️ Written using soap solution
➡️ On spraying → message appears in color
2. How can a gardener change the colour of hydrangea flowers?
๐ Answer:
๐ฑ Change soil pH:
- Acidic → blue ๐ต
- Basic → pink/red ๐ด
3. How can you identify vinegar, baking soda solution, and sugar solution using turmeric paper?
๐ Answer:
๐งช
- Baking soda → turns red ๐ด (basic)
- Vinegar & sugar → no change ๐ก
➡️ Vinegar = acidic, Sugar = neutral
4. Why did bubbles form when Aman spilled vinegar on eggshells?
๐ Answer:
๐ฅ Eggshell contains calcium carbonate
๐ถ Vinegar (acid) reacts → produces CO₂ gas
➡️ Bubbles form ๐ซง
5. Why is neutralisation useful in everyday life?
๐ Answer:
๐ Uses:
- Ant bite relief ๐
- Soil treatment ๐ฑ
- Waste treatment ๐ญ
- Antacids for stomach
➡️ Very important in daily life ๐ฏ
