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