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