Important Questions: Exploring Substances: Acidic, Basic, and Neutral | Science (Curiosity) Class 7 - New NCERT PDF Download

Q1: What is litmus obtained from?

a) Red roses
b) Lichens
c) Turmeric
d) Onions

Answer: b

Q2: What color does blue litmus paper turn when dipped in lemon juice?
a) Blue
b) Red
c) Green
d) Yellow

Answer: b

Q3: Which indicator turns red in basic substances?
a) Red rose extract
b) Blue litmus paper
c) Turmeric paper
d) Onion juice

Answer: c

Q4: What is the taste of acidic substances?
a) Bitter
b) Sour
c) Sweet
d) Salty

Answer: b

Q5: What does a neutralization reaction produce?
a) Sugar and water
b) Salt, water, and heat
c) Acid and base
d) Gas and light

Answer: b

Q6: Which substance is used to neutralize formic acid from an ant bite?
a) Lemon juice
b) Baking soda
c) Sugar solution
d) Vinegar

Answer: b

Q7: What color does red rose extract turn in a soap solution?
a) Red
b) Green
c) Yellow
d) Blue

Answer: b

Q8: Which natural indicator changes smell in acidic or basic substances?
a) Turmeric
b) Litmus
c) Onion juice
d) Red hibiscus

Answer: c

Q9: Why is turmeric called the ‘Golden Spice’?
a) Due to its bitter taste
b) For its golden color and health benefits
c) Because it grows in gold mines
d) For its high cost

Answer: b

Q10: What do hydrangea flowers indicate about soil in the Himalayas?
a) Soil temperature
b) Soil acidity or basicity
c) Soil color
d) Soil moisture

Answer: b

Q1: What is an indicator, and name two natural indicators mentioned in the story?

Answer: An indicator is a tool that changes color or smell to show if a substance is acidic, basic, or neutral. Two natural indicators are litmus and red rose extract.

Q2: How does red rose extract indicate acidic and basic substances?

Answer: Red rose extract turns red in acidic substances, like lemon juice, and green in basic substances, like soap solution, while remaining unchanged in neutral substances.

Q3: What is neutralization, and give one example from daily life?

Answer: Neutralization is the reaction between an acid and a base to form salt, water, and heat. An example is applying baking soda to an ant bite to neutralize formic acid.

Q4: Define “olfactory indicator” and provide an example.

Answer: An olfactory indicator changes smell in acidic or basic substances. An example is onion juice, which loses its smell when mixed with tamarind water or baking soda solution.

Q5: Why can’t turmeric paper distinguish between acidic and neutral substances?

Answer: Turmeric paper only turns red in basic substances and remains yellow in both acidic and neutral substances, making it unable to differentiate between them.

Q1: Explain how litmus and red rose extract work as acid-base indicators, with examples from the story.

Answer: Litmus, obtained from lichens, is used as blue and red paper strips. 

• Blue litmus turns red in acidic substances, like lemon juice.
• Red litmus turns blue in basic substances, like soap solution, while neutral substances, like sugar solution, cause no change. 

Red rose extract is a natural indicator made from crushed petals soaked in hot water.

• It turns red in acidic substances, such as lemon juice.
• It turns green in basic substances, like soap solution
• It remains unchanged in neutral substances. 

Both indicators help identify the nature of substances by changing color, with litmus being more specific for acids and bases, and red rose extract showing distinct shades for each, as seen in the science fair experiments.

Q2: Describe the neutralization process and its applications in daily life, with examples.

Answer: Neutralization is a chemical reaction where an acid and a base react in the right amounts to form salt, water, and heat, creating a neutral solution that doesn’t affect indicators. For example, mixing lemon juice (acidic) with lime water (basic) results in a neutral solution, as shown in the litmus activity where red litmus turns blue with added base. In daily life, neutralization is used to:

1. Relieve ant bites by applying baking soda (base) to neutralize formic acid, reducing pain.

2. Treat acidic soil with lime (base) to improve plant growth, or add organic matter to neutralize basic soil.

3. Neutralize acidic factory waste with bases before releasing it into lakes, protecting aquatic life.
   These applications show how neutralization balances substances for practical benefits.

Q3: Discuss the role of natural indicators in identifying substances, and why turmeric is limited as an indicator.

Answer: Natural indicators, like litmus, red rose extract, turmeric, and onion juice, help identify whether substances are acidic, basic, or neutral by changing color or smell. 

For example 

• Litmus turns blue to red for acids and red to blue for bases
• Red rose extract turns red for acids and green for bases
• Onion juice loses smell in acids or bases, while neutral substances cause no change. 

Turmeric is also a natural indicator. It is a yellow-colored substance commonly used in cooking, but it can also help identify whether a substance is acidic or basic.

• In an acidic or neutral solution → Turmeric stays yellow

• In a basic (alkaline) solution → Turmeric turns reddish-brown

 This makes turmeric is less useful than litmus or red rose extract as it can not clearly show the difference between acidic and neutral substances.