Page 111 - Basic physical chemistry for the atmospheric sciences

Acids and bases IJ'/

AgCl(s) +2 Ag + (aq) + Cl - ( aq) (5 . 2 91
Ag + (aq) + 2NH3 (aq) +2 Ag(NH3) ! (aq) (5 . 3 0)

Net: AgCl(s) + 2NH3(aq) +2 Ag(NH3} ! (aq) + Cl- (aq)
For the Lewis base NHiaq) to increase the solubility of AgCl(s) -
that i s , to drive reaction (5.29) to the right - it must interact more
strongly with Ag + (aq) than does water .
A metal ion combined with a Lewis base, such as Ag(NH ! h
(aq), is called a complex ion. The equilibrium constant fo r the forma­
tion of a complex ion from a metal ion in aqueous solution is called the
f o rmation constant (Kr ) of the complex ion. The higher the value of
Kc the more stable is the complex ion. Values of the formation con­
stants for some metal complex ions are given in Appendix IV.

5 . 1 1 Mass balance and charge balance relations
The ionization of any weak Br�nsted-Lowry acid HA is given by
Reaction (5 . 8 ), which, for convenience , we repeat here

Also ,
(5.32)
-
How can we calculate [HA(aq)] , [A ( aq)] , [H30 + (aq)] and [OH - ( aq)]
for a given initial concentration of HA in water? Since there are four
unknowns , we need four relationships between the unknowns .
The equilibrium constants for Reactions (5 . 3 l ) and (5 . 3 2 ) provide
two of the relationships
[H30 + (aq)][A - (aq)]
(5. 3 3)
K = �������
a [HA(aq)]
and,
Kw = [H30 + (aq)]l OH - (aq)] (5.34)

where the values of Ka and Kw are assumed to be known.
We can obtain a third relationship from the fact that the mass of HA
must be conserved. Therefore, we can write