CBSE Class 10 Science Chapter 2
Acids, Bases & Salts
Complete NCERT Notes
Key Definitions (100 Words Each)
1. Acid
Acids are substances that taste sour, turn blue litmus red, and react with metals to produce hydrogen gas. Chemically, they release H⁺ ions in water solution. HCl, H₂SO₄, HNO₃ are strong mineral acids. Organic acids like citric (lemon), acetic (vinegar), lactic (curd) found in food. Acids conduct electricity in solution. pH less than 7. React with bases to form salt + water (neutralization). Carbonic acid (H₂CO₃) in soda water very weak. Dil. acids react with carbonates/bicarbonates producing CO₂ gas. Used in batteries, cleaning, digestion. (98 words)
HCl + NaOH → NaCl + H₂O
2. Base
Bases taste bitter, feel slippery, turn red litmus blue, and react with acids to form salt + water. They release OH⁻ ions in water. NaOH (caustic soda), KOH (caustic potash) strong soluble bases. Metal oxides like CuO, ZnO insoluble bases. pH greater than 7. Conduct electricity when dissolved. Used in soap making, antacids, cleaning. Strong bases burn skin due to high reactivity with moisture. Weak bases like NH₄OH (ammonium hydroxide) used in smelling salts. React with non-metal oxides forming salts. Essential for neutralization reactions. (96 words)
NaOH + HCl → NaCl + H₂O
3. Salt
Salts formed by neutralization reaction between acid + base. Ionic compounds containing cation from base + anion from acid. NaCl (sodium chloride) common salt from HCl + NaOH. Salts can be neutral, acidic, or basic depending on acid/base strength. Baking soda (NaHCO₃), washing soda (Na₂CO₃), plaster of Paris (CaSO₄.½H₂O) important salts. Used in food preservation, water softening, medicine, construction. Soluble salts conduct electricity in solution. Crystal formation shows ionic nature. pH of salt solution depends on hydrolysis of ions. (92 words)
All NCERT Chemical Equations
| S.No |
Equation |
NCERT Reference |
| 2.1 | HCl + NaOH → NaCl + H₂O | Neutralization |
| 2.2 | Zn + H₂SO₄ → ZnSO₄ + H₂↑ | Acid + Metal |
| 2.3 | Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑ | Carbonate + Acid |
| 2.4 | NaHCO₃ + HCl → NaCl + H₂O + CO₂↑ | Baking Soda |
| 2.5 | Ca(OH)₂ + CO₂ → CaCO₃ + H₂O | White Washing |
| 2.6 | CaCO₃ → CaO + CO₂ (Heat) | Decomposition |
| 2.7 | CaO + H₂O → Ca(OH)₂ | Slaked Lime |
| 2.8 | CaSO₄.2H₂O → CaSO₄.½H₂O + 1½H₂O (Heat) | Plaster of Paris |
| 2.9 | CaSO₄.½H₂O + 1½H₂O → CaSO₄.2H₂O | Setting |
| 2.10 | NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃ | Solvay Process |
| 2.11 | 2NaCl + 2H₂O → 2NaOH + H₂↑ + Cl₂ | Chloralkali |
pH Scale & Indicators
| pH | Substance | Example |
|---|
| 0-2 | Strong Acid | HCl, H₂SO₄ |
| 3-6 | Weak Acid | Vinegar, Lemon |
| 7 | Neutral | Pure Water |
| 8-11 | Weak Base | Baking Soda |
| 12-14 | Strong Base | NaOH, KOH |
Indicators (NCERT)
- Blue Litmus → Red (Acid), Blue (Base)
- Red Litmus → Blue (Base), Red (Acid)
- Phenolphthalein → Pink (Base), Colourless (Acid)
- Methyl Orange → Red (Acid), Yellow (Base)
Types of Acids & Bases
Acids Classification
- Mineral Acids: HCl, H₂SO₄, HNO₃, H₃PO₄
- Organic Acids: Acetic (CH₃COOH), Citric, Lactic, Carbonic
- Strong Acids: Completely dissociate (HCl)
- Weak Acids: Partially dissociate (CH₃COOH)
Bases Classification
- Soluble Bases: Alkalis (NaOH, KOH, Ca(OH)₂)
- Insoluble Bases: Cu(OH)₂, Zn(OH)₂
Properties & Reactions
Acid Reactions (NCERT Activities)
Zn + H₂SO₄ → ZnSO₄ + H₂↑ (Pop sound)
Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑ (Brisk effervescence)
Mg + 2HCl → MgCl₂ + H₂↑
Base Reactions
CuO + 2HCl → CuCl₂ + H₂O
NH₃ + HCl → NH₄Cl
Important Salts (NCERT Focus)
| Salt | Chemical Name | Use |
|---|
| NaCl | Sodium Chloride | Table salt, preservation |
| NaHCO₃ | Sodium Bicarbonate | Baking powder, antacid |
| Na₂CO₃ | Sodium Carbonate | Washing soda, glass making |
| Na₂SO₄.10H₂O | Glauber's Salt | Medicine |
| CaSO₄.½H₂O | Plaster of Paris | Plastering, casts |
White Washing (NCERT Activity)
Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O
Slaked lime + CO₂ from air → Marble (CaCO₃) shining surface
Plaster of Paris
CaSO₄.2H₂O (Heat 373K) → CaSO₄.½H₂O + 1½H₂O
CaSO₄.½H₂O + 1½H₂O → CaSO₄.2H₂O (Sets as hard mass)
Uses: Plastering walls, doctor's casts, toys, statues
Board Exam Tips
- Write neutralization as acid + base → salt + water
- pH values: Strong acid <3, Strong base >11
- Plaster of Paris = CaSO₄.½H₂O
- Baking soda reaction produces CO₂ (bread rising)
- Chloralkali process: 2NaCl → NaOH + Cl₂ + H₂
- Always show state symbols in equations
✅ Complete NCERT Chapter 2 Coverage: All definitions, equations, activities, salts, pH scale, industrial processes.