Chapter 2 – Acids, Bases and Salts from Class 10 Science NCERT, with all important concepts and reactions:
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🔹 ACIDS
• Acids are substances that release H⁺ ions in aqueous solution.
• Taste: Sour
• Examples:
o Mineral acids: HCl, H₂SO₄, HNO₃
o Organic acids: Acetic acid (CH₃COOH), Citric acid
• Strong acids: Completely ionize in water (e.g., HCl)
• Weak acids: Partially ionize (e.g., CH₃COOH)
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🔹 BASES
• Bases are substances that release OH⁻ ions in aqueous solution.
• Taste: Bitter, slippery to touch
• Examples: NaOH, KOH, Ca(OH)₂
• Alkalis: Soluble bases (e.g., NaOH, KOH)
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🔹 INDICATORS
• Substances that change color in acids/bases:
o Litmus: Red in acid, Blue in base
o Methyl orange: Red in acid, Yellow in base
o Phenolphthalein: Colorless in acid, Pink in base
o Natural indicators: Turmeric, red cabbage
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🔹 REACTIONS OF ACIDS AND BASES
1. Reaction with Metals
Acid + Metal → Salt + H₂ gas
(Test for hydrogen: pop sound with burning match)
2. Reaction with Metal Carbonates/Bicarbonates
Acid + Metal carbonate → Salt + CO₂ + H₂O
3. Neutralisation Reaction
Acid + Base → Salt + Water
(Exothermic)
4. Reaction with Metal Oxides
Acid + Metal oxide → Salt + Water
(Metal oxides are basic)
5. Reaction of Non-metal Oxides with Bases
Non-metal oxide + Base → Salt + Water
(Non-metal oxides are acidic)
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🔹 PH SCALE
• pH measures hydrogen ion concentration.
• Scale: 0–14
o pH < 7 → Acidic
o pH = 7 → Neutral
o pH > 7 → Basic
• Lower pH → higher acidity
• Applications:
o Stomach acidity (HCl)
o Tooth decay: pH < 5.5
o Soil treatment: Use lime (Ca(OH)₂)
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🔹 SALTS
• Formed by neutralization of acid + base.
• Properties depend on parent acid and base.
• Examples:
o NaCl (common salt)
o NaHCO₃ (baking soda)
o Na₂CO₃ (washing soda)
o CaOCl₂ (bleaching powder)
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🔹 IMPORTANT SALTS AND THEIR USES
1. Sodium chloride (NaCl) – Common salt, food
2. Baking soda (NaHCO₃)
o Mild base
o Use: Baking, antacids, fire extinguishers
o Preparation: NaCl + NH₃ + CO₂ + H₂O → NH₄Cl + NaHCO₃
3. Washing soda (Na₂CO₃·10H₂O)
o Used in cleaning, softening hard water
o Obtained by heating baking soda
4. Bleaching powder (CaOCl₂)
o Disinfectant, bleaching agent
o Prepared by: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
5. Plaster of Paris (CaSO₄·½H₂O)
o Used for casts and molds
o Made by heating gypsum:
CaSO₄·2H₂O → CaSO₄·½H₂O + 1.5H₂O
o Reacts with water to form gypsum again
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