May 25, 2019, 03:22:32 PM
Forum Rules: Read This Before Posting


Topic: Calculating pH of a salt NaH2PO4?  (Read 20467 times)

0 Members and 1 Guest are viewing this topic.

Offline james_py

  • Very New Member
  • *
  • Posts: 1
  • Mole Snacks: +0/-0
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?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 25010
  • Mole Snacks: +1642/-395
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info, PZWT_s1

Sponsored Links