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Topic: Calculating pH of a salt NaH2PO4?  (Read 19922 times)

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Offline james_py

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Calculating pH of a salt NaH2PO4?
« on: December 02, 2011, 02:36:50 AM »
We are given that there 0.15M concentration of NaH2PO4. What is the pH?

And more importantly, Why can't I treat this as a regular weak acid problem and use an ICE table? (This is how we would solve for pH if it was 0.15M H3PO4.)

The CORRECT ANSWER is actually the average of pKa1 and pKa2: (1/2) (pKa1 + pKa2) = (1/2) (2.15+7.20) = 4.68

Why is this the correct answer? How can you just take the average of 2 pKas. And why CANT you use the ice table?

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