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pH shift in a Buffer Confusion

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I resently made a Tris-EDTA buffer that is displaying an increase in pH as heat is applied. 5°C-->7.8, 25°C-->8.0, 37°C-->8.3. WWWHHHYYYY? To the best of my understanding, increased heat should increase ionization resulting inan increase in[H+] and a decrease in pH.

Help please, TIO

By itself TrisH+ increases in pKa as the temperature decreases, and ΔpKa/ΔT is about -0.03 pH units per degree Celsius.  I would consider the possibility of an error in standardizing the pH meter, but I am just guessing.

Right, this might be a pH meter issue. Do you observe the same issue with just water?

I heard tris is dodgy with regular pH meters and should use Calomel ones. Anyone know anything about that?

Buffers:  The Basics (RJ Beyond) mentions that not all electrodes are compatible with Tris, but it does not supply more information than that.


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