PH: Difference between revisions

Revision as of 00:24, 5 November 2005

Revision as of 18:13, 5 November 2005

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* by using a [[pH meter]] together with pH-selective electrodes ([[pH glass electrode]], [[hydrogen electrode]], [[quinhydrone electrode]] and other).

pH ruined my life, it killed my rabbit. It stole my dog, and ate the lungs of my cat.

==pOH==

pH should go back to where it came from. All in Favor say I, all in disfavor say nay.

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There is also '''pOH''', in a sense the opposite of pH, which measures the concentration of OH^− ions. Since water self ionizes, and notating [OH^-] as the concentration of hydroxide ions, we have

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:<math>K_{w} = \left[ \mbox{H}^+ \right] \left[ \mbox{OH}^- \right] = 10^{-14}</math> (*)

where K_w is the ionization constant of water.

Now, since

:<math>\log_{10}K_{w} = \log_{10} \left[ \mbox{H}^+ \right] + \log_{10} \left[ \mbox{OH}^- \right]</math>

by [[logarithmic identities]], we then have the relationship

:<math>-14 = \log_{10} \left[ \mbox{H}^+ \right] + \log_{10} \left[ \mbox{OH}^- \right]</math> (*)

and thus

:<math>\mbox{pOH} = -\log_{10} \left[ \mbox{OH}^- \right] = 14 + \log_{10} \left[ \mbox{H}^+ \right] = 14 - \mbox{pH}</math> (*)

(*) Valid exactly for temperature = 298.15 K (25 °C) only, acceptable for most lab calculations.

==Calculation of pH for weak and strong acids==