Summary Topic 5 - Acid-Base Equilibria

Chemistry
Topic 5: Acid-Base Equilibria

Recap
Acid + metal  salt + hydrogen
Acid + base  salt + water
Acid + alkali  salt + water
Acid + carbonate  salt + water + carbon dioxide

Brønsted-Lowry acid is a proton (H+), donor
Brønsted-Lowry base is a proton (H+), acceptor

HCl – monobasic
H2SO4 – Dibasic
H3PO4 – Tribasic

Conjugate acid-base pairs

An acid is related to its conjugate base by the fact that the acid has one more hydrogen ion than its
conjugate base.

A base is related to its conjugate acid H3O+ by the fact that the base has one hydrogen ion less than its
conjugate acid.

Example
H2O + HCl ⇌ H3O+ + Cl-
Acid -----> conjugate base
Base ----------> conjugate acid

Acid Conjugate base Base Conjugate acid
H2SO4 HSO4- NH3 NH4+
HNO3 NO3- H2O H3O+
H2O OH- HSO4- H2SO4-
CH3CO2H CH3CO2- SO42- HSO4-

An acid-base pair is a pair of two species that transform into each other by gain or loss of a proton.




The acidity of a solution depends on the concentration of [H + (aq)] and is measured on the pH scale.

pH = -log[H+(aq)]

The relationship between pH and [H+(aq)] has a ‘see-saw’ relationship – when one goes up, the other goes
down. A low pH means a high [H+(aq)] and vice versa.

Strong and weak acids
The strength of an acid HA is the extent of its dissociation of H + and A- ions.