Indicators in Chemistry

Study Notes

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.

Description

This quiz explores the concept of indicators in chemistry, focusing on their role in determining the acidic or basic nature of solutions. Learn about the types of indicators, including natural indicators like litmus and turmeric, and their applications in identifying pH levels.