Acids, Bases, and Salts

Introduction to Acids and Bases

• Acids: Sour in taste, examples include:
  • Curd: Lactic acid
  • Lemon: Citric acid
  • Vinegar: Acetic acid
• Bases: Bitter in taste and soapy to touch, found in:
  • Detergents
  • Toothpaste
  • Hair dyes

Testing for Acids and Bases

Acid-Base Indicators

• Natural Indicators:
  • Litmus (from lichens):
    • Blue litmus turns red in acid
    • Red litmus turns blue in base
  • Other examples: Red cabbage, turmeric, hibiscus
• Synthetic Indicators:
  • Methyl orange: Red in acid, yellow in base
  • Phenolphthalein: No change in acid, turns pink in base

Olfactory Indicators

• Examples: Onion, vanilla essence, clove oil
• Experiment with onion:
  • Chopped onions placed in a cloth, produce acidic vapors.
  • Acid treatment retains onion smell, base treatment loses it.

Reactions of Acids and Bases

Reaction with Metals

• Acid + Metal: Produces salt + hydrogen gas.
  • Example: Zinc + dilute HCl → Zinc sulfate + H₂
• Base + Metal: Produces salt + hydrogen gas.
  • Example: Zinc + concentrated sodium hydroxide → Sodium zincate + H₂

Reaction of Metal Carbonates with Acids

• Metal Carbonate + Acid: Produces salt + water + carbon dioxide.
  • Example: Sodium carbonate + dilute HCl → Sodium chloride + CO₂ + H₂O
• Gas produces white precipitate with calcium hydroxide.

Reaction of Metal Hydrogen Carbonates with Acids

• Same as carbonates, producing salt, water, and CO₂.

Neutralization Reactions

• Acid + Base: Produces salt + water.
  • Experiment with sodium hydroxide and HCl shows neutralization.

Reaction of Metal Oxides with Acids

• Metal Oxide + Acid: Produces salt + water.
• Example: Copper oxide + HCl → Copper chloride + water.

Reaction of Non-Metal Oxides with Bases

• Base + Non-metal oxide: Produces salt + water.
  • Example: Calcium hydroxide + CO₂ → Calcium carbonate (precipitate).

Conductivity of Acids and Bases

• Acids and bases conduct electricity in solution due to ion production.
  • Example: HCl → H⁺ + Cl⁻; NaOH → Na⁺ + OH⁻.

Dilution of Acids and Bases

• Mixing with water decreases ion concentration, releases heat.
• Safety Advice: Always add acid to water, never the reverse.

Strength of Acids and Bases (pH Scale)

• pH scale: 0 (strong acids) - 14 (strong bases).
  • pH 7: Neutral.
• Importance of pH:
  • Aquatic life requires specific pH for survival.
  • Stomach acidity important for digestion; antacids used to reduce acidity.

Acids and Bases in Nature

• Self-defense: Living organisms like wasps use acidic stings that can be neutralized with bases.

Salts

• Classification of salts:
  • Neutral: Strong acid + strong base (pH 7).
  • Acidic: Strong acid + weak base (pH < 7).
  • Basic: Weak acid + strong base (pH > 7).

Common Salt (Sodium Chloride)

• Used to produce various chemical compounds such as:
  • Caustic Soda (Sodium hydroxide)
  • Baking Soda
  • Washing Soda
  • Bleaching Powder

Processes Involving Sodium Chloride

• Chlor-Alkali Process: Electolysis of sodium chloride produces NaOH, Cl₂, H₂.
• Uses of products:
  • Chlorine gas: Water treatment, disinfectants.
  • Hydrogen gas: Fuel, margarine production.
  • Sodium hydroxide: Soaps, paper industry.

Baking Soda (NaHCO₃)

• Produced by reacting common salt with ammonia and carbon dioxide.
• Used as an antacid, in baking, and in fire extinguishers.

Washing Soda (Na₂CO₃)

• Produced by recrystallization of sodium carbonate.
• Used in glass, soap, and cleaning agents.

Bleaching Powder (Ca(OCl)₂)

• Produced by reacting chlorine gas with calcium hydroxide.
• Used in whitening fabrics, disinfecting.

Plaster of Paris (CaSO₄·1/2H₂O)

• Produced by heating gypsum.
• Used in medical applications, toys, models.

Conclusion

• Understanding acids, bases, and salts is important in daily life, science, and industry.

Key Terms: Acids, Bases, pH, Neutralization, Salts, Electrolysis, Chlor-Alkali process.