Acid, Base, and Salts - Class 10 Science Chapter 2

Introduction

• Discuss physical and chemical properties of acids, bases, and salts.
• Reactions, nature, and additional information.

Basic Definitions

• Acids:
  • Sour taste.
  • Turn blue litmus to red.
  • Release H+ ions in aqueous solutions (e.g., HCl, H2SO4).
• Bases:
  • Bitter taste.
  • Turn red litmus to blue.
  • Release OH- ions in aqueous solutions (e.g., NaOH).
• Salts:
  • Formed by neutralization reactions between acids and bases.
  • E.g., NaCl.

Types of Acids and Bases

• Based on Occurrence:
  • Organic acids (e.g., citric acid) and inorganic acids (e.g., HCl).
  • Organic bases (e.g., pyridine) and inorganic bases (e.g., NaOH).
• Based on Strength:
  • Strong acids (completely dissociate, e.g., HCl) and weak acids (partially dissociate, e.g., acetic acid).
  • Strong bases (completely dissociate, e.g., NaOH) and weak bases (partially dissociate, e.g., ammonia).
• Based on Concentration:
  • Concentrated acids/bases (less water). E.g., concentrated HCl.
  • Dilute acids/bases (more water). E.g., dilute HCl.

Indicators

• Substances that change color/smell in the presence of acids/bases.
• Types:
  • Natural Indicators:
    • Litmus: Red in acid, blue in base.
    • Turmeric: No change in acid, red in base.
  • Synthetic Indicators:
    • Methyl orange: Red in acid, yellow in base.
    • Phenolphthalein: Colorless in acid, pink in base.
  • Olfactory Indicators:
    • Vanilla essence: Smell in acid, no smell in base.
    • Clove oil: Increased smell in acid, decreased smell in base.

Chemical Properties of Acids and Bases

• Reaction With Metals:
  • Acid + Metal → Salt + Hydrogen gas.
  • Base + Metal → Salt + Hydrogen gas.
• Reaction With Metal Carbonates/Hydrogen Carbonates:
  • Acid + Metal Carbonate → Salt + CO2 + Water.
  • Acid + Metal Hydrogen Carbonate → Salt + CO2 + Water.
• Reaction With Each Other (Neutralization):
  • Acid + Base → Salt + Water.
  • Called neutralization reactions; forms H2O.
• Reaction of Metallic Oxides with Acids:
  • Metal oxides are basic; react with acids to form salt and water.
• Reaction of Non-Metallic Oxides with Bases:
  • Non-metallic oxides are acidic; react with bases to form salt and water.

Universal Indicator and pH Scale

• Universal Indicator:
  • Mixture of indicators showing different colors at different pH levels.
  • pH scale (0-14): Measures acidity/basicity.
• pH Values:
  • <7: Acidic (stronger acid: lower pH, e.g., pH 1-3).
  • 7: Neutral (e.g., NaCl solution).

  • 7: Basic (stronger base: higher pH, e.g., pH 11-14).

Importance of pH in Daily Life

• Human body effective pH: 7-7.8.
• Acid rain: pH <5.6.
• Tooth decay: pH <5.5.
• Plant growth requires specific pH.

Salts

• Ionic compounds formed by neutralization reactions.
• Example: NaCl (table salt).

Important Chemical Compounds

• Sodium Hydroxide (NaOH)
  • Known as caustic soda.
  • Formed by decomposition of NaCl in water (electrolysis).
  • Uses: Manufacturing soap, paper, refining oil, making PVC, etc.
• Bleaching Powder (CaOCl2)
  • Formed by reaction of chlorine with dry slaked lime.
  • Uses: Bleaching cotton/linen, disinfecting drinking water, oxidizing agent.
• Baking Soda (NaHCO3)
  • Formed by reaction of NaCl, water, CO2, and NH3.
  • Uses: Making cold drinks, fire extinguishers, antacid, baking powder.
• Washing Soda (Na2CO3·10H2O)
  • Formed by heating baking soda and adding water molecules.
  • Uses: Cleaning agent, removing water hardness.
• Plaster of Paris (CaSO4·½H2O)
  • Formed by heating gypsum.
  • Uses: Making smooth surfaces, toys, supporting fractured bones.

Conclusion

• Understanding acids, bases, and salts is crucial for their practical applications in daily life.