Acids, Bases, and Salts

1. Definitions of Acids and Bases

1.1 Arrhenius Definition

• Acid: A substance that increases the concentration of $H^+$ (or $H_3O^+$) ions in water.
  Example: $$HCl \rightarrow H^+ + Cl^-$$
• Base: A substance that increases the concentration of $OH^-$ ions in water.
  Example: $$NaOH \rightarrow Na^+ + OH^-$$

1.2 Bronsted-Lowry Definition

• Acid: A proton donor.
• Base: A proton acceptor.
  Example: Ammonia acts as a base by accepting $H^+$: $$NH_3 + H_2O \rightarrow NH_4^+ + OH^-$$

1.3 Lewis Definition

• Acid: An electron pair acceptor.
• Base: An electron pair donor.
  Example: Boron trifluoride ($BF_3$) accepts an electron pair from ammonia ($NH_3$).

2. Physical and Chemical Properties of Acids and Bases

2.1 Physical Properties

• Acids: Sour taste, corrosive, turn blue litmus red.
• Bases: Bitter taste, slippery feel, turn red litmus blue.

2.2 Chemical Properties

1. Reaction with Metals: $$2HCl + Zn \rightarrow ZnCl_2 + H_2$$
2. Reaction with Metal Carbonates: $$2HCl + Na_2CO_3 \rightarrow 2NaCl + CO_2 + H_2O$$
3. Neutralization Reaction: $$HCl + NaOH \rightarrow NaCl + H_2O$$

3. Acids, Bases, and Salts as Electrolytes

• Electrolytes: Substances that conduct electricity in aqueous solution.
• Strong Electrolytes: Fully dissociate in water (e.g., $HCl, NaOH$).
• Weak Electrolytes: Partially dissociate in water (e.g., $CH_3COOH, NH_3$).

4. Classification of Acids and Bases

4.1 Classification of Acids

• Strength:
  • Strong: Completely ionize (e.g., $HCl, H_2SO_4$).
  • Weak: Partially ionize (e.g., $CH_3COOH$).
• Basicity: Number of replaceable $H^+$:
  • Monobasic: $HCl$.
  • Dibasic: $H_2SO_4$.
  • Tribasic: $H_3PO_4$.

4.2 Classification of Bases

• Strength:
  • Strong: Fully ionize (e.g., $NaOH, KOH$).
  • Weak: Partially ionize (e.g., $NH_3$).
• Basicity: Monoacidic, diacidic, triacidic.

5. Concept of pH

• pH: A measure of the hydrogen ion concentration: $$pH = -\log[H^+]$$
• Scale: Ranges from 0 (acidic) to 14 (basic), with 7 as neutral.
• Measurement: pH meters, universal indicators, or colorimetric methods.
• Applications:
  • Soil pH for agriculture.
  • Blood pH (7.35–7.45) for health.

6. Salts

6.1 Types of Salts

• Normal Salts: Complete neutralization (e.g., $NaCl$).
• Acid Salts: Partial neutralization (e.g., $NaHSO_4$).
• Basic Salts: Excess base remains (e.g., $Bi(OH)_2NO_3$).
• Double Salts: Contain two cations (e.g., alum).
• Complex Salts: Contain a central metal ion (e.g., $K_4[Fe(CN)_6]$).

6.2 Preparation of Salts

1. Laboratory Methods:
   • Neutralization (acid + base): $$HCl + NaOH \rightarrow NaCl + H_2O$$
   • Precipitation (mixing two solutions): $$AgNO_3 + NaCl \rightarrow AgCl (s) + NaNO_3$$
2. Industrial Production:
   • Extraction of sodium chloride and its conversion to NaOH, $Cl_2$, and $H_2$.

6.3 Hydrolysis of Salts

• Salt solutions can be acidic, basic, or neutral depending on their hydrolysis.
  Example: $$NH_4Cl + H_2O \rightarrow NH_4^+ + OH^- \; (\text{acidic solution})$$

7. Deliquescent, Efflorescent, and Hygroscopic Compounds

• Deliquescent: Absorb moisture and dissolve (e.g., $NaOH$).
• Efflorescent: Lose water of crystallization (e.g., $Na_2CO_3 \cdot 10H_2O$).
• Hygroscopic: Absorb moisture but do not dissolve (e.g., $CaCl_2$).

8. Acid-Base Indicators

• Definition: Weak organic acids/bases that change color at specific pH ranges.
• Examples:
  • Methyl orange (pH 3.1–4.4): Red to yellow.
  • Phenolphthalein (pH 8.3–10.0): Colorless to pink.

9. Acid-Base Titration

9.1 Apparatus and Procedure

• Apparatus: Burette, pipette, conical flask.
• Procedure: Measure acid/base, add indicator, titrate until endpoint.

9.2 Applications

• Determining concentration, molar ratios, and water of crystallization.
• Example: $$H_2SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O$$

10. Summary

• Acids and bases play vital roles in chemical reactions, industry, and biological systems.
• Salts are crucial in food, agriculture, and pharmaceuticals.
• pH control is essential in environmental science and healthcare.

Understanding these concepts helps to analyze chemical behavior and solve practical problems efficiently.