Chemistry Reference
In-Depth Information
Moles of
Free Ca
per liter
Increasing
complexing ability
(i.e., less free Ca ions)
Figure 9.1.
The free calcium concentration (i.e. not chelated or sequestered) for various types
of complexing agents are estimated for the dissociation of a 0.01 M solution of the 1:1 Ca
complex. Complexing agents that are lower on the scale (e.g. EDTA) are stronger chelators for
calcium (adapted from Van Wazer and Callis, 1958).
stability constant of a metal (e.g. Ca
2+
) complex can be calculated as follows
(Furia, 1972):
K
¼
M
½
½½
where M is the metal ion, L is the ligand (sequestrant, chelating agent) and
ML is the metal complex.
The (log K) stability constants for Ca-chelates with citrate, pyropho-
sphate and EDTA are 3.5, 5.0 and 10.7, respectively (Furia, 1972). Higher
values indicate a stronger tendency to form a complex.
