This in-depth summary for Unit 1 Acid-Base Equilibria is synthesized directly from the new
Ethiopian Grade 12 Chemistry curriculum It focuses on the conceptual evolution of acid-base
theories and the unique chemical behaviors that define the modern understanding of the
subject
1 The Theoretical Evolution Beyond Arrhenius
While the Arrhenius concept was the first successful attempt to define acids and bases its
limitation is its strict reliance on aqueous water solutions and the requirement for bases to
contain a hydroxide OH group
The Bronsted-Lowry Shift Introduced in 1923 this theory defines acids and bases through
proton H transfer
Acid A proton donor
Base A proton acceptor
The Nuance This theory explains why substances like Ammonia NH3 act as bases even
though they lack OH In this framework a base does not just exist it functions by accepting a
proton which simultaneously turns the donor into a conjugate base
The Lewis Electronic View This is the most inclusive definition focusing on electron pairs
rather than protons
Acid An electron-pair acceptor
Base An electron-pair donor
The Insight Many species without any hydrogen at all such as metal ions or molecules like
BCl3 act as Lewis acids because they have electron-deficient atoms
2 The Duality of Water Auto-ionization and Amphiprotism
Water is chemically unique because it is amphiprotic it can act as both an acid and a base
depending on what it reacts with
Molecular Auto-ionization Even in pure water molecules are constantly colliding and
transferring protons to one another 2H2O yields H3O + OH
The Ion-Product Constant Kw At 25C the product of the concentration of hydronium and
hydroxide ions is always 1.0 x 10^-14 This equilibrium is the foundation of the entire pH
scale
Amphiprotic Species Beyond water ions like Bicarbonate HCO3 or Dihydrogen Phosphate
H2PO4 can either donate or accept a proton making them versatile players in biological
buffering systems
3 The Dynamics of Weak Electrolytes
Ethiopian Grade 12 Chemistry curriculum It focuses on the conceptual evolution of acid-base
theories and the unique chemical behaviors that define the modern understanding of the
subject
1 The Theoretical Evolution Beyond Arrhenius
While the Arrhenius concept was the first successful attempt to define acids and bases its
limitation is its strict reliance on aqueous water solutions and the requirement for bases to
contain a hydroxide OH group
The Bronsted-Lowry Shift Introduced in 1923 this theory defines acids and bases through
proton H transfer
Acid A proton donor
Base A proton acceptor
The Nuance This theory explains why substances like Ammonia NH3 act as bases even
though they lack OH In this framework a base does not just exist it functions by accepting a
proton which simultaneously turns the donor into a conjugate base
The Lewis Electronic View This is the most inclusive definition focusing on electron pairs
rather than protons
Acid An electron-pair acceptor
Base An electron-pair donor
The Insight Many species without any hydrogen at all such as metal ions or molecules like
BCl3 act as Lewis acids because they have electron-deficient atoms
2 The Duality of Water Auto-ionization and Amphiprotism
Water is chemically unique because it is amphiprotic it can act as both an acid and a base
depending on what it reacts with
Molecular Auto-ionization Even in pure water molecules are constantly colliding and
transferring protons to one another 2H2O yields H3O + OH
The Ion-Product Constant Kw At 25C the product of the concentration of hydronium and
hydroxide ions is always 1.0 x 10^-14 This equilibrium is the foundation of the entire pH
scale
Amphiprotic Species Beyond water ions like Bicarbonate HCO3 or Dihydrogen Phosphate
H2PO4 can either donate or accept a proton making them versatile players in biological
buffering systems
3 The Dynamics of Weak Electrolytes
