log Kw = -4470.99/T + 6.0875 - 0.01706 T
Temperature affects both the ionization of water and the ionization of the acid, so Ka will vary with temperature too. Depending onMost acid-base titrations are done at room temperature for convenience (glassware is usually calibrated for 20°C), and when people say "Kw is 1.01×10-14" or "pH + pOH = 14", they're talking about room temperature. These numbers are easy to remember and they're appropriate for most situations you'll encounter in general chemistry. It's an i you'll often find undotted.
But consider calculating the pH of blood plasma inside a living organism. You'd have to take the temperature variation of Kw into account (pKw is 13.60 at body temperature (37°C), and 13.996 at room temperature (25°C)). It's a little more difficult to take into account the temperature variation of the various Ka's in the plasma buffering system. The analysts just measure the pH at 37°C rather than taking the measurement at a different temperature and bothering with a temperature correction.
Copyright © 1997-2010 by Fred Senese
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Last Revised 02/23/18.URL: http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/print-temperature-dependence-Kw.shtml