๐ Class 7 Science Curiosity – Chapter 2 Notes
๐งช Exploring Substances: Acidic, Basic, and Neutral | Amresh Academy
๐ Introduction
This chapter explains acidic, basic, and neutral substances ๐งช
๐ It begins with a science fair experiment where a hidden message appeared due to a chemical reaction, creating curiosity about indicators.
๐ฟ 1. Nature – Our Science Laboratory
๐ด Litmus as an Indicator
๐ What is Litmus?
- Natural substance from lichens (fungus + algae)
- Available as:
- Blue paper ๐ต
- Red paper ๐ด
- Used as an acid-base indicator
⚡ How it Works:
- ๐ Acidic substances → Blue litmus turns red
- ๐งผ Basic substances → Red litmus turns blue
- ๐ง Neutral substances → No change
๐งช Examples:
๐ด Acidic:
- Lemon juice
- Amla juice
- Tamarind water
- Vinegar
๐ต Basic:
- Soap solution
- Baking soda
- Lime water
- Washing powder
⚪ Neutral:
- Tap water
- Sugar solution
- Salt solution
๐งฑ Lime Water:
- Made from calcium oxide + water
- Allowed to settle and filtered
๐น 2. Red Rose as an Indicator
๐ธ Red Rose Extract:
- Works as natural indicator
๐ Color changes:
- Acid → Red ๐ด
- Base → Green ๐ข
- Neutral → No change
๐ฟ Other Natural Indicators:
- Beetroot
- Purple cabbage
- Turmeric
- Jamun
- Hibiscus
๐บ Fascinating Fact:
๐ Hydrangea flower color changes:
- Acidic soil → Blue ๐ธ
- Basic soil → Pink/Red ๐ธ
๐ก 3. Turmeric as an Indicator
๐ง Properties:
- Turns red in basic solutions ๐ด
- Remains yellow in acidic/neutral ๐ก
๐ Fact:
๐ Turmeric is a “Golden Spice”
- Used in food ๐
- Ayurvedic medicine ๐ฟ
๐ Olfactory Indicators
๐ Substances whose smell changes
Example:
- Onion smell changes with:
- Acid (tamarind)
- Base (baking soda)
⚖️ 4. Neutralization Reaction
๐งช Definition:
๐ When acid + base combine → neutral solution
๐ Reaction:
๐ Acid + Base → Salt + Water + Heat
๐ก Example:
- Lemon juice (acid) + Lime water (base)๐ Forms neutral solution
๐ 5. Neutralization in Daily Life
๐ Ant Bite:
- Contains formic acid
- Baking soda (base) neutralizes it
๐ฑ Soil Treatment:
- Acidic soil → add lime
- Basic soil → add organic matter
๐ญ Industrial Waste:
- Acidic waste treated with bases๐ Protects aquatic life
๐ญ 6. Science Fair Mystery
๐ Hidden message appeared due to turmeric indicator
๐ง Explanation:
- Written with base (soap solution)
- Sprayed with turmeric → turns red๐ Message becomes visible
๐ 7. Key Points
- Substances are:
- Acidic ๐ด
- Basic ๐ต
- Neutral ⚪
๐งช Indicators:
- Litmus → Red/Blue change
- Red rose → Red/Green
- Turmeric → Yellow/Red
- Olfactory → Smell change
๐ Properties:
- Acids → Sour taste
- Bases → Bitter + slippery
- Neutral → No effect
⚖️ Neutralization:
๐ Acid + Base → Salt + Water + Heat
๐ 8. Common Acids in Food
Food Item | Acid |
Lemon ๐ | Citric acid |
Curd ๐ฅ | Lactic acid |
Tamarind ๐ฐ | Tartaric acid |
Vinegar ๐งด | Acetic acid |
๐จ๐ฌ 9. Know a Scientist
๐ Acharya Prafulla Chandra Ray
- Father of Modern Indian Chemistry ๐ฎ๐ณ
- Studied in UK ๐
- Founded India’s first pharma company (1901)
- Promoted Indian culture & education
๐ Final Summary
๐ This chapter helps you understand:
- Acids, bases & neutral substances ๐งช
- Indicators ๐ฟ
- Neutralization ⚖️
- Daily life applications ๐
