📌 Key Points
- Acids taste sour and release hydrogen ions (H+) when dissolved in water.
- Bases taste bitter, feel slippery/soapy, and release hydroxide ions (OH-) in water.
- Blue litmus paper turns red in acids; red litmus paper turns blue in bases.
- Mineral acids (HCl, H2SO4, HNO3) are strong acids prepared artificially from minerals.
- Organic acids (citric, acetic, lactic) are weak acids found naturally in plants and animals.
- Water-soluble bases are called alkalis. All alkalis are bases, but not all bases are alkalis.
- Indicators like litmus, phenolphthalein, and turmeric help identify acids and bases.
- Phenolphthalein is colourless in acids and turns pink in bases.
- Turmeric remains yellow in acids but turns red/brown in bases.
- The pH scale measures acidity/basicity: pH < 7 is acidic, pH = 7 is neutral, pH > 7 is basic.
- Neutralization: Acid + Base produces Salt + Water + Heat.
- Antacids (bases) neutralize excess stomach acid to relieve acidity.
- Bee sting is acidic - apply baking soda (base); wasp sting is basic - apply vinegar (acid).
- Fire extinguisher uses acid + carbonate reaction to produce CO2 which puts out fire.
- Acidic soil is treated with lime (calcium hydroxide) to neutralize it for crops.
📘 Important Definitions
🔢 Formulas & Laws
Neutralization Reaction
Acid + Base → Salt + Water + Heat
Example: HCl + NaOH → NaCl + H2O
Fire Extinguisher Reaction
Na2CO3 + H2SO4 → Na2SO4 + CO2 + H2O
Sodium carbonate + Sulphuric acid produces carbon dioxide
⚠️ Common Mistakes
✗ Wrong: All bases are alkalis.
✓ Correct: Only bases that dissolve in water are called alkalis. All alkalis are bases, but not all bases are alkalis.
✗ Wrong: pH 0 is neutral because it is the lowest number.
✓ Correct: pH 7 is neutral. pH below 7 is acidic (lower = more acidic), pH above 7 is basic (higher = more basic).
✗ Wrong: Bee sting should be treated with vinegar (acid).
✓ Correct: Bee sting injects formic acid (acidic), so apply baking soda (base) to neutralize. Wasp sting is basic, so use vinegar.
✗ Wrong: Litmus paper changes colour in neutral solutions.
✓ Correct: Neutral solutions (pH 7) do not change the colour of either blue or red litmus paper.
✗ Wrong: Strong acids are found naturally in fruits.
✓ Correct: Fruits contain organic acids which are weak acids. Strong acids (mineral acids like HCl, H2SO4) are prepared artificially.
📝 Exam Focus
These questions are frequently asked in CBSE exams:
Diagram to practice: Practice drawing: (1) pH scale showing acidic, neutral, and basic ranges, (2) Soda-acid fire extinguisher showing inner and outer chambers, (3) Table showing indicator colours in acids and bases.
🎯 Last-Minute Recall
Close your eyes and try to recall: Key definitions, formulas, and 3 common mistakes. If you can recall 80% without looking, you're exam-ready!