Lecture Notes: Acids, Bases, and Salts

Definitions

• Acid: Proton donor; donates H⁺ ions in a reaction.
• Base: Proton acceptor; reacts to form OH⁻ ions when dissolved in water.
• Alkali: A base that dissolves in water.
• Salt: Ionic substance formed from the reaction of an acid with a base.

Key Concepts

• Proton (H⁺): In the context of acids, refers to a hydrogen ion, which is a hydrogen atom that has lost its electron.
• Concentration: A concentrated solution has a small amount of water; a dilute solution has a large amount of water.

Types of Acids and Bases

• Strong Acid: Fully ionizes in solution (e.g., HCl, H₂SO₄).
• Weak Acid: Partially ionizes in solution (e.g., CH₃COOH).
• Strong Base: Fully ionizes in solution (e.g., NaOH, KOH).
• Weak Base: Partially ionizes in solution (e.g., NH₃).

pH Scale

• Ranges from 0 to 14.
• Acids: pH < 7
  • Strong acid: pH 1-3
  • Weak acid: pH 4-6
• Neutral: pH = 7 (e.g., water, NaCl solution)
• Bases: pH > 7
  • Strong base: pH 11-14
  • Weak base: pH 8-10

Identifying Acids and Bases

• Acids often start with an "H" (e.g., HCl).
• Bases often end with "OH" or contain "O" (e.g., NaOH, CaO).

Reactions

• Neutralization: Acid + Base → Salt + Water
• Acid + Metal: Acid + Metal → Salt + Hydrogen gas
• Acid + Carbonate: Acid + Carbonate → Salt + CO₂ + Water
• Base + Ammonium Salt: Base + Ammonium Salt → Ammonia gas + Water

Indicators

• Litmus:
  • Acid: Red
  • Base: Blue
• Universal Indicator: Provides a range of colors to indicate pH level.
• Phenolphthalein:
  • Base: Pink
  • Neutral/Acid: Colorless
• Methyl Orange:
  • Acid: Red
  • Base: Yellow
  • Neutral: Orange

Oxides

• Acidic Oxides: Generally non-metal oxides (e.g., CO₂, SO₂).
• Basic Oxides: Generally metal oxides (e.g., CaO, MgO).
• Amphoteric Oxides: Reacts with both acids and bases (e.g., Al₂O₃, ZnO).
• Neutral Oxides: Do not react with acids or bases (e.g., CO, N₂O).

Preparation of Salts

• Titration: Used when both reactants are soluble.
• Neutralization: Used when starting reactant is insoluble.
• Precipitation: Used to form insoluble salts.

Sample Reactions and Questions

• Neutralization Example: Reaction of HCl with NaOH to form NaCl.
• Precipitation Example: Formation of AgCl from AgNO₃ and NaCl.
• Sample Questions: Includes predicting products and identifying pH changes.

Note: Always balance chemical equations and understand the context of the reactions (acid, base, neutral, etc.).