🔬 Chapter 2 — Exploring Substances: Acidic, Basic, and Neutral
Class 7 Science | Curiosity | EduGrown Notes
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⚗️ The colourful world of Acidic, Basic and Neutral substances!
⚗️ Acids, Bases & Neutral Substances
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🔴Acidic substances = Turn blue litmus paper RED | Taste sour | e.g., lemon juice, vinegar, tamarind
🔵Basic substances = Turn red litmus paper BLUE | Taste bitter, feel soapy/slippery | e.g., soap, baking soda, lime water
⚪Neutral substances = Do NOT change colour of either litmus | e.g., water, salt solution, sugar solution
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🔬 Blue litmus turns red in acids, red litmus turns blue in bases!
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⚗️ Science fair — exploring colourful world of substances
📜 Litmus — The Classic Indicator
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🌿Litmus = natural dye extracted from lichens (fungi + algae)
📜Available as blue litmus paper and red litmus paper
🔴Acid → turns blue litmus red
🔵Base → turns red litmus blue
⚪Neutral → does not change the colour of either litmus paper
🌹 Natural Indicators
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🌹Red rose extract — changes colour in acids (pink/red) and bases (green/yellow)
🫐Many coloured flowers, fruits, and vegetables can serve as natural acid-base indicators
💡These are prepared by crushing petals in hot water and filtering — the filtrate is the indicator!
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🌹 Red rose petals — a natural acid-base indicator!
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⚗️ Rose extract changes colour in acid vs base
🍋 Common Acids & Bases Around Us
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| Substance | Nature | Acid/Base Present |
|---|---|---|
| 🍋 Lemon juice | Acidic | Citric acid + Ascorbic acid |
| 🍇 Grapes/Tamarind | Acidic | Tartaric acid |
| 🍎 Amla | Acidic | Ascorbic acid (Vitamin C) + Citric acid |
| 🥗 Spinach/Tomato | Acidic | Oxalic acid + Citric acid |
| 🧼 Soap solution | Basic | Sodium/Potassium hydroxide |
| 🍪 Baking soda | Basic | Sodium bicarbonate |
| 🧹 Washing soda | Basic | Sodium carbonate |
| 💧 Water, Salt, Sugar | Neutral | Neither acid nor base |
💡 Easy Memory Trick!
Acid → Acid turns blue litmus Red (A → B→R)
Base → Base turns red litmus Blue (B → R→B)
Acids taste SOUR (khatta) | Bases feel SOAPY/SLIPPERY and taste BITTER (kadwa)
🚨 Never taste unknown substances! Use indicators instead.
Base → Base turns red litmus Blue (B → R→B)
Acids taste SOUR (khatta) | Bases feel SOAPY/SLIPPERY and taste BITTER (kadwa)
🚨 Never taste unknown substances! Use indicators instead.
⚗️ Neutralisation — Acid + Base = Salt + Water
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🔄When an acid and a base mix together, they cancel each other out → Neutralisation
🧪Products formed: Salt + Water
🌿Example: Acid soil (too acidic for farming) → treated with lime (basic) to neutralise → good for crops!
💊Antacids (medicines for acidity) = bases that neutralise excess stomach acid
🐝Bee sting (acidic) → apply baking soda (basic) to neutralise the pain!
⭐ Quick Summary
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📝 Key Points
🔴Acid = sour taste, turns blue litmus RED (lemon, vinegar, tamarind, amla)
🔵Base = bitter/soapy, turns red litmus BLUE (soap, baking soda, lime water)
⚪Neutral = no change in litmus (water, salt solution, sugar solution)
📜Litmus = from lichens | Natural indicators: rose extract, turmeric, china rose
🔄Neutralisation: Acid + Base → Salt + Water (antacids, bee sting treatment, soil correction)