guy - 7-6-2006 at 15:15
pH is derived from the nernst equation where Q is [H+]<sup>2</sup>/H<sub>2</sub> and H2 is at 1atm. Solving for pH, you get
-log[H+]. The question is that, when measuring for pH, why don't you need 1 atm of H2 around?
12AX7 - 7-6-2006 at 15:27
Erm, you're measuring hydrogen ions, not dissolved hydrogen?
H2O <--> H+ + OH- doesn't give up any hydrogen gas, so there's no need to measure it with a pressure of H2.
Tim
guy - 7-6-2006 at 15:40
2e + 2H+ <--> H2
E = (-0.059/2) log([H+]<sup>2</sup>/[H2]) when H2 = 1 atm
E = -0.059 log[H+]
pH = E/0.059 = -log[H+]
[Edited on 6/7/2006 by guy]
12AX7 - 7-6-2006 at 16:31
Yeah, but I think that's redox, not pH. You're measuring two different things AFAIK.
Or is this about the thing where you put an electrode in, and it gets some voltage (compared to...something) corresponding to the pH? I remember
something about microvolt amplifiers and a teensy little electrode probe thing...
Tim
Magpie - 8-6-2006 at 13:17
I was under the impression that pH is defined as "-log[H+]."
Doesn't the Nernst equation just set up the conditions necessary to obtain a standard voltage?
guy - 8-6-2006 at 14:13
Yeah I figured it out