Acids, Bases, and
Acid-Base Equilibria
Brønsted-Lowry
theory
• Proposed by J.N. Brønsted in
Denmark and T.M. Lowry in Great
Britain in 1923.
• According to Bronsted-Lowry
Theory, ”an acid is a *proton
donor and a base is a proton
acceptor.”
• However, substance cannot simply
shed a proton, because proton
cannot exist in a solution as a free
particle.
*Proton is simply an ionized hydrogen atom
Conjugate Acid-Base Pair
Identify the Brønsted-Lowry acid and base pair and their
conjugates in
(a) H2S + NH3
(b) OH- + H2PO4(c) NH3 + HCO3(d) H3PO4 + H2O
NH4+ + HSH2O + HPO42NH4+ + CO32H2PO4- +H3O+
• Water is an amphiprotic substance –
acid and base property, enabling the
transfer of proton from one water
molecule to another – self-ionization.
Self-Ionization of
Water – pH Scale
Consider the self-ionization of water:
2H2O (l)
H3O+ (aq) + OH- (aq)
At 25 °C, the experimentally determined
equilibrium concentrations in pure water are [H3O+]
= [OH-] = 1.0 x 10 -7 M.
Determine the [OH-] of HCl if it has 0.00015 M of
H3O+?
pH/pOH
• In 1909, the Danish biochemist Søren
Sørenson proposed a convenient
convention that is still used today.
• pH is refer as “power of hydrogen”
• [H+] = 10 –pH
• pH = -log [H3O+]
Sample Problem
1. Determine the pH of HCl if it has
0.00015 M of H3O+?
2. What is the pH and pOH of a 2.5 x 10 -3
M NaOH solution that has [OH-] = 2.5 X
10-3 ?