Overview of Acids and Bases

Definitions and Theories

Arrhenius Definition

• Acids: Substances that increase the concentration of H+ ions in a solution.
• Bases: Substances that increase the concentration of OH- ions in a solution.
• Example Reaction:
  • HCl(aq) → H+(aq) + Cl-(aq)
  • NaOH(aq) → Na+(aq) + OH-(aq)

Limitations

• Does not explain substances that do not contain OH- ions but make basic solutions (e.g., NH3).
• Limited to aqueous solutions.

Brønsted-Lowry Definition

• Acids: Proton (H+ ion) donors.
• Bases: Proton (H+ ion) acceptors.
• Example Reaction:
  • HCl (donates H+) + NH3 (accepts H+) → NH4+ + Cl-
• Amphoteric: Substances that can act as both acids and bases.

Conjugate Acids and Bases

• Every acid has a conjugate base, and vice versa.
• Example:
  • HCl (acid) → Cl- (conjugate base)
  • NH3 (base) → NH4+ (conjugate acid)

Lewis Theory

• Acids: Electron pair acceptors.
• Bases: Electron pair donors.
• Example Reaction:
  • NH3 (donates electrons) + BF3 (accepts electrons) → H3NBF3

Strength of Acids and Bases

Strong Acids and Bases

• Strong Acids: Ionize completely in solution (e.g., HCl, HNO3).
• Strong Bases: Disassociate completely in solution (e.g., NaOH, KOH).

Weak Acids and Bases

• Do not ionize completely in solution (e.g., acetic acid, ammonia).

pH Scale

• Measures acidity and basicity based on H+ ion concentration:
  • pH = -log[H+]
• pH < 7: Acidic
• pH > 7: Basic
• pH = 7: Neutral

Neutralization

• Reaction of acids and bases to form water and a salt.
• General Reaction: Acid + Base → H2O + Salt

Titrations

• Used to determine the concentration of an acid or base.
• Equivalence point: moles of acid = moles of base.
• Example Calculation:
  • Molarity(acid) * Volume(acid) = Molarity(base) * Volume(base)

Exercises

1. Identify strong acids: HNO3 (strong), others are weak or not acids.
2. Identify Brønsted-Lowry bases: HPO4^2- (amphoteric).
3. Calculate concentration of HCl via titration example.
4. Determine concentration of NaOH from neutralization reaction.
5. Identify Brønsted-Lowry base but not Arrhenius base: NH3.

References

1. Brent, Lynnette. Acids and Bases.
2. Hulanicki, Adam. Reactions of Acids and Bases in Analytical Chemistry.
3. Oxlade, Chris. Acids & Bases.
4. Petrucci, Ralph H. General Chemistry: Principles and Modern Applications.
5. Vanderwerd, Calvin A. Acids, Bases, and the Chemistry of the Covalent Bond.

This overview provides a comprehensive understanding of the different theories and definitions related to acids and bases, how they interact, and their strengths, complemented by practical exercises for better understanding.