Introduction to Acids and Bases

Presenter: Chad from Chad's Prep

This lesson is an introduction to acids and bases, part of a general chemistry series. The lesson will cover:

• Definitions of acids and bases
• Conjugate acids and bases
• Strong vs. weak acids and bases

Definitions of Acids and Bases

Three main definitions used historically:

1. Arrhenius Definition

   • Acids increase the concentration of H3O+ in aqueous solutions.
   • Bases increase the concentration of OH- in aqueous solutions.
   • Limited to aqueous solutions.
   • Example: HCl increases H3O+ when dissolved in water.

2. Bronsted-Lowry Definition

   • Acids are proton (H+) donors.
   • Bases are proton (H+) acceptors.
   • Not limited to water; includes reactions in other solvents or gas phase.
   • Example: HCl in gas phase can act as a Bronsted-Lowry acid.

3. Lewis Definition

   • Acids are electron pair acceptors.
   • Bases are electron pair donors.
   • Includes reactions where new bonds are formed to atoms other than hydrogen.
   • Example: Boron compounds as Lewis acids.

Conjugate Acids and Bases

• Conjugate Acid-Base Pair: Two species in equilibrium where one acts as an acid and the other as a base.
• Identified by Bronsted-Lowry definitions:
  • Conjugate base is what remains after an acid donates a proton.
  • Conjugate acid is formed when a base accepts a proton.
• Amphiprotic species can act as both acids and bases (e.g., bicarbonate HCO3-).

Strong vs. Weak Acids and Bases

Strong Acids

• Dissociate completely in water.
• Common strong acids: HCl, HBr, HI, HNO3, H2SO4, HClO4, and sometimes HClO3.
• The leveling effect: all strong acids appear to have the same strength in water.

Weak Acids

• Do not dissociate completely.
• Example: HF, acetic acid (CH3COOH).
• HF is a weak acid despite being commonly perceived as strong due to its corrosive properties.

Strong Bases

• Typically metal hydroxides.
• Group 1 metal hydroxides: LiOH, NaOH, KOH, RbOH, CsOH.
• Group 2 metal hydroxides (less soluble): Mg(OH)2, Ca(OH)2, Sr(OH)2, Ba(OH)2.

Weak Bases

• Common example: Ammonia (NH3).
• Organic amines derived from ammonia.

Relevance of Acid-Base Strength

• Strong acids/bases dissociate completely, affecting solution pH.
• Weak acids/bases dissociate partially; their concentration impacts dissociation level.

Conclusion

• Understanding the definitions and differences between strong and weak acids/bases is crucial for further study in chemistry.

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