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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: james_py on December 02, 2011, 02:36:50 AM

Title: Calculating pH of a salt NaH2PO4?
Post by: james_py 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?

Title: Re: Calculating pH of a salt NaH2PO4?
Post by: Borek on December 02, 2011, 03:00:52 AM

http://www.chembuddy.com/?left=pH-calculation&right=pH-amphiprotic-salt