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Transcript 
 pH effect on EDTA titration
• Note that the metal–EDTA complex
becomes less stable as pH decreases and
Kf decreases.
[Ca2+]=2.7×10-6 M at pH 10.0
[Ca2+]=3.5×10-4 M at pH 6.0
• In order to get a “complete”(say, 99.9%)
titration, EDTA requires a certain minimum
pH for the titration of each metal ion.
Ex) pH effect for the titration of Ca2+
⇒ Below pH≈8, the end point is not sharp
enough to allow accurate determination.
(∵The K for CaY2- is just too small for
“complete” reaction at low pH.)
Minimum pH for Effective
Titration of Metal Ions
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