Homework Help: Chemistry

Posted by Alba on Friday, February 22, 2013 at 4:01pm.

pKa1 = 2.148, pKa2 = 7.198, pKa3 = 12.375

You wish to prepare 1.000L of a 0.0100M Phosphate buffer at pH7.55. To do this, you choose to use mix the two salt fomrs involved in the second ionization, NaH2PO4 and Na2HPO4, in a 1.000L volumetric flask and add water to the mark. What mass of each salt will you add to the mixture?

mass NaH2PO4 and Na2HPO4?

What other combination of phosphoric acid and /or its salt could be mixed to prepare this buffer?
*Check all that apply*

a) H3PO4 and NaH2PO4
b) H3PO4 and Na2HPO4
c) H3PO4 and Na3PO4
d) NaH2PO4 and Na3PO4
e) Na2HPO4 and Na3PO4

Chemistry - DrBob222, Friday, February 22, 2013 at 5:52pm
You have two unknowns so you need two equations.
pH = pK2 + log(base)/(acid)
Substitute the number and solve for base/acid for one equation.
The second is base + acid = 0.1M

Post your work if you get stuck.

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