PH and Solubility

M) -4

FIGURE 9-13 Solubility of CaC03 as a function of pH.

0 -

-2 -

«

-4 -

Fe(OH)3

u a

-6 -

(solid) ^

u 6C

-8 -

hJ

Fe(OH)2

10

^^ Fe(OH)4

14

FIGURE 9-14 Solubility of amorphous Fe(OH)3 as a function of pH. Increased slope of the solubility plot at pH values below about 4 is due to the formation of Fe(OH)2+ and other species rather than Fe(OH)+ at high acidity.

(nonamphoteric) and ferric hydroxide (amphoteric). In the latter case, solubility increases at high pH as soluble Fe(OH)4 forms. At low pH, solubilty increases through the formation of soluble cationic species.

Lead carbonate can be used as an example to show how the solubility depends on pH in a quantitative way.5 The solubility product of PbCO3, given from

gives the solubilty of Pb2+ as 2.72 x 1047 M. However, in the presence of acid, the reaction is

This is just the difference of reactions (9-30) and (9-24), and the equilibrium constant for reaction (9-31) is

0 0

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