Acid-base equilibria
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Hi. I was wondering if a pH of any substance changes with a change in temperature?
Also, if there is a change of pH in the substance, what substance would it be? The temperature range is preferably 0 to 100 degrees Celcius.
130808
Corrie writes .....
One obvious type of substance that springs to mind is a weak acid. In solution an equilibrium will exist due to partial dissociation of the weak acid:
HA(aq) <=> H+(aq) + A-(aq), where HA is a typical monobasic weak acid, such as ethanoic acid.
Now, assuming the enthalpy change for this dissociation reaction is not zero, then the above equilibrium should, according to Le Chatelier's principle, be affected by a change in temperature.
If the enthalpy change for dissociation reaction is endothermic, then increasing the temperature should move the equilibrium to the right, increasing the H+ ion concentration and thus lowering the pH of the solution - and vice versa.
Whether this effect will be large enough to be measurable will depend on the size of the enthalpy change and the change in temperature. It's worth a try?!
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updated: 14 August 2008
