2 the pka ph when the titrant added is 12 the volume needed to get to the equivalence point say

First, we need to identify the equivalence points for the first two protons. These are the point

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2. The pKa = pH when the titrant added is ½ the volume needed to get to the equivalence point. Say the equivalence point is at 30.0mL of titrant. The pH at 15.0mL will be equal to the pKa of the acid. With a diprotic acid, the next equivalence point would be at 60.0mL and the pKa2 would be 45.0mL of titrant. Looking at your titration curve for phosphoric acid, determine the equivalence points for the first two protons, then using the logic stated above, determine where the third equivalence point should be on the graph. Look up the pKa3 for phosphoric acid and determine if you can find it on your graph.

          2.	The pKa = pH when the titrant added is ½ the volume needed to get to the equivalence point.  Say the equivalence point is at 30.0mL of titrant.  The pH at 15.0mL will be equal to the pKa of the acid.  With a diprotic acid, the next equivalence point would be at 60.0mL and the pKa2 would be 45.0mL of titrant.  Looking at your titration curve for phosphoric acid, determine the equivalence points for the first two protons, then using the logic stated above, determine where the third equivalence point should be on the graph.  Look up the pKa3 for phosphoric acid and determine if you can find it on your graph.

Added by Kitty K.

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