ACIDS/BASES AND KW
ACID AND BASE STRENGTHS
•Taken from State University of West Georgia Chemistry
ACID AND BASE STRENGTHS
•Taken from State University of West Georgia Chemistry Dept.
HYDRONIUM IONS
HYDRONIUM IONS
H5O2+
DISSOCIATION OF WATER
H2O + H2O <---> H3O1+ + OH1 The equilibrium expression is products over
reactants.



The molarity for the water is a constant at any
specific temperature. So


K [H2O] [H2O] = [H3O1+] [OH1-]
The quantity on the right hand side of the
equation is formally defined as Kw. The
numerical vale for Kw is different at different
temperatures.


K = [H3O1+] [OH1-] / [H2O] [H2O]
At 25oC Kw = 1.014 x 10-14
Kw = K[H2O] [H2O] or Kw = [H3O1+] [OH1-]
DISSOCIATION OF WATER
 Equilibrium
constants exist then for
both acid dissociation and base. (Ka
and Kb)
 The higher the Ka, the stronger the
acid and the higher the Kb, the
stronger the base.
 Ka and Kb are related by the
previous equation.
 K w = K aK b
DISSOCIATION OF WATER
As
Ka gets larger the
strength of the acid gets
higher, but Kb must
fall. Therefore the stronger
the acid, the weaker the
conjugate base.
DISSOCIATION OF WATER
It
can now be said that the
conjugate base (acid) of a weak
acid (base) is a weak base (acid)
and the conjugate base (acid) of
a strong acid (base) is a
worthless base (acid).
DISSOCIATION OF WATER
The
strength of an acid/base is
usually given as a pKa value. As
pKa is inversely related to Ka,
the higher the Ka (the stronger
the acid), the lower the pKa
value. The same is true of bases.
CALCULATING PH
-log [H+]
Power of Hydronium (Hydrogen)
P[OH-] = - log [OH]
THE PH SCALE
PH IN
SOLUTIONS OF STRONG ACIDS
AND STRONG BASES
 Strong
acids
 Certain acids are known as strong acids.
These are acids that fully ionize when
placed in water:

HA + H2O  A- + H3O+
 Goes to completion and thus
 Ka = [A-][H3O+]/[HA] = infinity
 Some common strong
 HCl, hydrochloric acid
 HBr, hyrdobromic acid
 HI, hydroiodic acid
 H2SO4, sulfuric acid
 HNO3, nitric acid
 HClO4, perchloric acid
acids are:
PH IN
SOLUTIONS OF STRONG ACIDS
AND STRONG BASES
Strong Bases
 Certain bases are known as strong bases. These
are bases that fully ionize when placed in water.
 Some common strong bases are:

LiOH, lithium hydroxide
 NaOH, sodium hydroxide
 KOH, potassium hydroxide
 Ca(OH)2, calcium hydroxide
 Sr(OH)2, strontium hydroxide
 Ba(OH)2, barium hydroxide


Alkaline earth oxides.

Lime (CaO)