What is the pH behavior with temperature?

Question

I don't know the very effect of temperature on pH when misure it with my pHmeter.

Answer 1

Good question!

You have to remember that water is never pure. In other words, you will never have just H2O. H+ and OH- ions will exist as free ions in suspension around the H2O compounds.
When you increase the temperature, the H+ ions will dissociate into the air at a greater rate than the OH- ions. Having more OH- ions in solution will give a higher pH.

So, increasing the temperature of water, will slowly raise the pH.

Answer 2

pH is affected by temperature.
For pure water you have the equillibrium

H2O <=> H(+) +OH(-)

with Kw=10^-14 at room temperature.
The scale of pH is from 0 to pKw and neutrality at 0.5pKw

When you increase temperature the equillibrium shifts to the right and thus Kw increases. E.g. you can go to Kw=10^-13 (don't remember exactly for which temperature) so then you have the scale from 0 to 13 and neutrality at 6.5

When you have buffers you change more than one equillibria. Therefore for each buffering system the change in the pH is different. For example for Tris-HCl you have dpH/dTemp= -0.028 pH units/deg Celsius and for glycine-NaOH you have -0.026.

Depending on what you want to do you might be able to tolerate slight inaccuracies (a few degrees C will not be so dramatic). If you have to be extremely accurate you need to control the temperature, use for calibration buffers for which you know the change in pH and set properly the settings in your pH-meter.

Answer 3

LOL,
I wouldn't accept anything from wikipedia as a definitive answer for this question. OK, yes the number of H ions increases with temperature. However, the same number of OH ions increases at the same rate. H and OH ions are just split water molecules. The ratio of H to OH is the same no matter the temperature. The Ph scale itself is built around the neutrality of water (7.0).

Answer 4

pH = - log [H3O+] where [H3O+] is concentration of H3O+ ions.
Eg. In pure water you have the equillibrium :
2 H2O <===> H3O+ + OH-
it is a reverse reaction, and it is endothermic (or exothermic, but probably endothermic, sorry, I dont remember). According to Le Chatelier principle in higer temperature the equilibrium would shift and more H3O+ and OH- will be produced. Since pH is -log[H3O+] , the pH will decrease. There are more OH- as well, but it doesn't matter - pH is a negative log of [H3O+].

Answer 5

Yes, temperature has a factor.
Water pH gets smaller with higher temperatures.

http://en.wikipedia.org/wiki/PH

Answer 6

pH is the negative log of [H+] to base 10
[H+] is not dependant on temperature { only in case of weak electrolytes[it is dependant on concentration and degree of dissociation(which is dependant on temp)] and in case of strong electrolytes it is not since [H+]=basicity *concentration}

Answer 7

well, no real behaviour.I mean pH is not affected by temperature.