[Krashy]

Hi guys, need help with calculating pH from this problem:

1,40 grams sodium dihydrogen phosphate (NaH2PO4) has been dissolved in 500 mL of water.
Assume in this problem that the dissolution of a solid in a liquid will not lead to an increase in the volume of that liquid.

a) Give the equations for the acid-base reactions that are possible between H2O and H2PO4-


H2O + H2PO4-     ------>  H3PO4 + OH-


b) Point out whether the described solution is acidic, basic or neutral responding.


500 g H2O x 1 mol H2O   = 27.75 mol H2O
                  18.02 g H2O

1.40 g NaH2PO4 x 1 mol NaH2PO4   = 0.012 mol NaH2PO4
                          119.98 g NaH2PO4


M = 0.012 / 0.5 L
M = 0.024

pH = -log 0.012

pH = 1.92

-> so its acidic (?)

I think this problem is not so hard, i´m probably just too stupid thanks for help 

[AWK]

a) Give the equations...

There are two different equations nedded for approximate pH calculation of this salt.

Problem is not so stupid - pH should be close to 4.5.

[Borek]

Hint: google for pH of amphiprotic salt.