acids salts and bases

Topic 11.1: Acids, Bases & Salts

Definitions

  • Acids: Proton donors (H+ donors)

  • Bases: Proton acceptors (H+ acceptors)

  • Neutral Solutions: Solutions that are neither acidic nor basic

Types of Acids and Bases

  • Strong Acid: Completely ionized in water; high concentration of H+ ions. Examples: HCl, HNO3, H2SO4

  • Weak Acid: Partially ionized in water; low concentration of H+ ions. Example: CH3COOH

  • Strong Base: Completely ionized in water; high concentration of OH- ions. Examples: NaOH, KOH

  • Weak Base: Partially ionized in water; low concentration of OH- ions. Example: NH3

Properties

  • Acids: Sour taste, pH < 7, turn blue litmus paper red.

  • Bases: Soft & slippery, pH > 7, turn red litmus paper blue.

  • Alkali: Soluble bases in water.

Most Common Acids and Bases

  • Acids: Hydrochloric (HCl), Nitric (HNO3), Sulfuric (H2SO4), Ethanoic (CH3COOH)

  • Bases: Sodium Hydroxide (NaOH), Potassium Hydroxide (KOH), Calcium Hydroxide (Ca(OH)2), Ammonia (NH3)

pH Scale

  • Acids: pH 1-6 (Strong: 1-3; Weak: 4-6)

  • Neutral: pH 7

  • Bases: pH 8-14 (Weak: 8-10; Strong: 12-14)

Measuring pH

  1. pH Meter: Digital instrument for exact pH.

  2. Universal Indicator: Color changes indicate pH.

    • Lower pH: Darker colors (Yellow → Orange → Red)

    • Neutral: Green (pH 7)

    • Higher pH: Darker colors (Blue → Dark Blue → Purple)

Chemical Reactions of Acids

  • Reactions: Acids react with Metals, Bases, Metal Carbonates, and Ammonia to form salts.

  • Displacement Reactions: Reactive metals displace hydrogen from acids.

Example Reactions

  • Zinc + Sulfuric Acid → Zinc Sulfate + Hydrogen:

    • Equation: H2SO4 + Zn → ZnSO4 + H2

  • Magnesium + Hydrochloric Acid → Magnesium Chloride + Hydrogen:

    • Equation: Mg + 2 HCl → MgCl2 + H2

Indicators

  • Litmus Paper: Red in acid, blue in alkaline

  • Methyl Orange: Red in acid, yellow in alkaline

  • Phenolphthalein: Colorless in acid, pink in alkaline

Neutralization Reactions

  • Acids + Bases → Salts + Water

  • Reactions produce neutral products, usually exothermic.

Examples

  1. Base + Acid → Salt + Water

    • KOH + HNO3 → KNO3 + H2O

  2. Metal Carbonate + Acid → Salt + Water + Carbon Dioxide

    • CaCO3 + 2 HCl → CaCl2 + H2O + CO2

  3. Ammonia + Acid → Ammonium Salt

    • NH3 + HCl → NH4Cl

Preparation of Salts

Solubility of Salts

  • Soluble Salts: All nitrates are soluble; some sulfates and chlorides are exceptions.

  • Insoluble Salts: Most metal hydroxides and carbonates are insoluble except those of Li, Na, K, NH4.

Preparation Methods

  1. Excess Method: For soluble salts (not Li, Na, K, NH4).

    • Example: Preparation of Zinc Sulfate.

  2. Titration Method: For Li, Na, K, NH4 salts.

    • Example: Preparation of Sodium Chloride.

Important Q&A

  • Why warm the acid? To increase reaction rate.

  • How to know the reaction is finished? Excess solid remains; no gas bubbles.

  • Why stir the mixture with glass rod? Glass doesn't react with acids, unlike metal.

  • Cooling to form crystals? Solubility decreases with temperature lowering.

Precipitation Reaction

  • Definition: Mixing solutions containing positive and negative ions creates an insoluble solid (precipitate).

  • Example: Preparation of Silver Chloride.

    • AgNO3 (aq.) + NaCl (aq.) → AgCl (s) + NaNO3 (aq.)