ЁЯМЯ Class 7 Science Curiosity – Chapter 2 Solutions
ЁЯзк Exploring Substances: Acidic, Basic and Neutral | Amresh Academy
ЁЯУЭ ЁЯФ╣ Question 1
1. A solution turns the red litmus paper to blue. Excess addition of which of the following solution would reverse the change?
ЁЯСЙ Answer: (iii) Vinegar ЁЯНЛ
ЁЯУЭ ЁЯФ╣ 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?
ЁЯСЙ Answer: (iv) Basic, basic and basic ⚡
ЁЯСЙ Explanation:
- A → Red litmus turns blue → Basic ЁЯз╝
- B → Turmeric turns red → Basic ЁЯЯе
- C → Rose extract turns green → Basic ЁЯЯв
ЁЯУЭ ЁЯФ╣ 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.
ЁЯСЙ Answer:
- Fig. 2.13 → Acidic ЁЯФ┤
- Fig. 2.14 → Basic ЁЯЯв
- Fig. 2.15 → Neutral ⚪
ЁЯСЙ Explanation:
- Red rose extract turns red in acid
- Turns green in base
- Shows no change in neutral solution
ЁЯУЭ ЁЯФ╣ 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.
ЁЯСЙ Justification:
- It turns blue litmus red ЁЯФ┤, which confirms acidic nature
- No change in turmeric also supports this
ЁЯУЭ ЁЯФ╣ 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?
ЁЯСЙ Explanation:
- She cannot see color changes
- Olfactory indicators change smell, which she can detect ✔️
ЁЯУЭ ЁЯФ╣ 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.
ЁЯСЙ Answer:
Writing Solution ✍️ | Spraying Liquid ЁЯТз | Colour ЁЯОи |
Soap solution (Basic) | Turmeric solution | Red ЁЯФ┤ |
Lime water (Basic) | Turmeric solution | Red ЁЯФ┤ |
Baking soda solution (Basic) | Turmeric solution | Red ЁЯФ┤ |
Soap solution (Basic) | Red rose extract | Green ЁЯЯв |
Lemon juice (Acidic) | Red rose extract | Red ЁЯФ┤ |
Vinegar (Acidic) | Red rose extract | Red ЁЯФ┤ |
Lemon juice (Acidic) | Blue litmus solution | Red ЁЯФ┤ |
ЁЯУЭ ЁЯФ╣ 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.
ЁЯСЙ Explanation:
- Grape juice is acidic ЁЯНЗ → turns rose extract red
- Baking soda is basic ЁЯз╝
- Adding base → neutralisation → then basic → turns green
ЁЯУЭ ЁЯФ╣ 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?
ЁЯСЙ Explanation:
- Orange juice is acidic ЁЯНК
- Indicators will change color → message becomes visible
ЁЯУЭ ЁЯФ╣ Question 9
9. How can natural indicators be prepared? Explain by giving an example.
ЁЯСЙ Example (Red Rose Extract ЁЯМ╣):
- Collect petals
- Wash and crush them
- Add hot water
- Filter the solution
ЁЯСЙ This coloured solution acts as an indicator ✔️
ЁЯУЭ ЁЯФ╣ 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.
ЁЯСЙ Explanation:
- Baking soda → turns turmeric red ЁЯЯе (basic)
- Vinegar → no change (acidic)
- Sugar → no change (neutral)
ЁЯУЭ ЁЯФ╣ 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?
ЁЯСЙ Answer:
- Liquid X is basic ЁЯЯв
- Adding amla juice (acidic ЁЯНЛ) → solution becomes acidic
ЁЯСЙ Indicator will turn red ЁЯФ┤
ЁЯУЭ ЁЯФ╣ Question 12
12. Observe and analyse the information given in the following flowchart. Complete the missing information.
ЁЯСЙ Answer:
- Soil acidic → add lime ЁЯзк
- Soil basic → add organic matter ЁЯМ┐
- Indicator → litmus / soil test kit
✍️ ЁЯФ╣ Very Short Answer Type Questions
1. What surprising thing happened with Ashwin and Keerthi at the science fair?
ЁЯСЙ Answer:
✨ Their white sheets showed the message “Welcome to the Wonderful World of Science” after being sprayed with a liquid.
ЁЯдп This made them curious and excited about science experiments.
2. What is litmus obtained from?
ЁЯСЙ Answer:
ЁЯМ┐ Litmus is obtained from lichens (a combination of fungus and algae).
ЁЯУД It is available as red and blue paper strips or solution.
3. What does a substance turning blue litmus paper red indicate?
ЁЯСЙ Answer:
ЁЯФ┤ It indicates that the substance is acidic in nature.
4. What does a basic substance feel like when touched?
ЁЯСЙ Answer:
ЁЯз╝ Basic substances feel slippery or soapy when touched (e.g., baking soda solution).
5. What is an olfactory indicator?
ЁЯСЙ Answer:
ЁЯСГ Olfactory indicators are substances whose smell changes in acidic or basic conditions (e.g., onion).
ЁЯза ЁЯФ╣ Short Answer Type Questions
1. What do we learn by grouping samples into Group A, B, and C in the litmus test?
ЁЯСЙ Answer:
ЁЯУК
- Group A → Acidic (blue litmus → red ЁЯФ┤)
- Group B → Basic (red litmus → blue ЁЯФ╡)
- Group C → Neutral (no change ⚪)
➡️ Helps in easy classification of substances
2. How does red rose extract work as an indicator?
ЁЯСЙ Answer:
ЁЯМ╣
- Acidic → turns red ЁЯФ┤
- Basic → turns green ЁЯЯв
- Neutral → no change
➡️ It is a natural indicator
3. How is turmeric used as an indicator?
ЁЯСЙ Answer:
ЁЯМ╝ Turmeric paper:
- Basic → turns red ЁЯФ┤
- Acidic/Neutral → remains yellow ЁЯЯб
4. What happens in a neutralisation reaction?
ЁЯСЙ Answer:
⚖️ Acid + Base → Salt + Water + Heat
ЁЯФе This reaction releases heat and forms a neutral solution
5. Why did moist baking soda help Ashwin after an ant bite?
ЁЯСЙ Answer:
ЁЯРЬ Ant injects formic acid
ЁЯзк Baking soda (base) neutralises it
➡️ Pain gets relieved ЁЯШМ
ЁЯУЦ ЁЯФ╣ Descriptive Answer Type Questions
1. Explain how soil treatment helps plants grow better.
ЁЯСЙ Answer:
ЁЯМ▒
- 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?
ЁЯСЙ Answer:
ЁЯПн Acidic waste harms aquatic life ЁЯРЯ
➡️ Adding base neutralises it
ЁЯМН Protects environment and water life
3. Why can’t turmeric be used to test acidic substances?
ЁЯСЙ Answer:
ЁЯМ╝ 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?
ЁЯСЙ Answer:
ЁЯМ╕
- Acidic soil → Blue flowers ЁЯФ╡
- Basic soil → Pink/Red flowers ЁЯФ┤
➡️ Indicates soil nature
5. Why should we not taste unknown substances during experiments?
ЁЯСЙ Answer:
⚠️ Unknown substances may be poisonous or harmful
➡️ Always follow safety rules in lab ЁЯзк
ЁЯЪА ЁЯФ╣ Exploring Type Questions
1. How could Ashwin’s “secret greeting card” trick work?
ЁЯСЙ Answer:
ЁЯОи 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?
ЁЯСЙ Answer:
ЁЯМ▒ Change soil pH:
- Acidic → blue ЁЯФ╡
- Basic → pink/red ЁЯФ┤
3. How can you identify vinegar, baking soda solution, and sugar solution using turmeric paper?
ЁЯСЙ Answer:
ЁЯзк
- Baking soda → turns red ЁЯФ┤ (basic)
- Vinegar & sugar → no change ЁЯЯб
➡️ Vinegar = acidic, Sugar = neutral
4. Why did bubbles form when Aman spilled vinegar on eggshells?
ЁЯСЙ Answer:
ЁЯеЪ Eggshell contains calcium carbonate
ЁЯН╢ Vinegar (acid) reacts → produces CO₂ gas
➡️ Bubbles form ЁЯлз
5. Why is neutralisation useful in everyday life?
ЁЯСЙ Answer:
ЁЯМН Uses:
- Ant bite relief ЁЯРЬ
- Soil treatment ЁЯМ▒
- Waste treatment ЁЯПн
- Antacids for stomach
➡️ Very important in daily life ЁЯТп
