Indicators in Chemistry

Indicators

• Substances that indicate acidity or basicity of a solution through color change.

Types of Indicators

Natural Indicators

• Derived from natural sources.
• Common examples include:
  • Litmus: Obtained from lichens; purple in solution.
    • Blue litmus turns red in acid; red turns blue in base.
  • Turmeric: Yellow in color.
    • Turns reddish-brown with a base; no color change with acid.
  • Red Cabbage: Purple juice.
    • Changes to reddish with acid; greenish with base.

Olfactory Indicators

• Change smell when mixed with acids or bases.
• Notable examples:
  • Onion: Loses odor when added to base; retains smell with acid.
  • Vanilla: Smell disappears with base; unaffected by acid.

Synthetic Indicators

• Created in the laboratory.
• Examples include:
  • Phenolphthalein: Colorless in acid; turns pink in base.
  • Methyl Orange: Orange initially; appears red in acid and yellow in base.

Acids

• Characterized by sour taste and the ability to turn blue litmus red; they dissociate to release H+ ions in water.
• Common examples:
  • Sulphuric acid (H2SO4)
  • Acetic acid (CH3COOH)
  • Nitric acid (HNO3)

Properties of Acids

• Sour taste.
• Blue litmus turns red.
• Conduct electricity in solution.
• Release H+ ions when dissolved in water.

Types of Acids

• Natural (Organic) Acids: Obtained from natural sources.
  • Examples:
    • Methanoic acid (HCOOH)
    • Acetic acid (Vinegar)
    • Citric acid (Citrus fruits)
• Mineral Acids: Prepared from minerals; also known as inorganic or synthetic acids.
  • Examples:
    • Hydrochloric acid (HCl)
    • Sulphuric acid (H2SO4)
    • Nitric acid (HNO3)

Chemical Properties of Acids

• Reaction with Metals: Produces hydrogen gas and respective salt.

  • For example, reaction of hydrochloric acid with zinc yields zinc chloride and hydrogen gas.

• Reaction with Metal Carbonates: Yields carbon dioxide gas, water, and respective salts.

  • Example with hydrochloric acid and sodium carbonate results in sodium chloride, carbon dioxide, and water.

Testing for Hydrogen Gas

• Presence of hydrogen gas confirmed by bringing a lighted candle near the test; it burns with a pop sound, indicating hydrogen evolution.