[Link The Worlds]

I'm really lost for this assignment and don't even know where to begin...

I'm supposed to describe the preparation of 15 liters of .07 M phosphate buffer, pH 7.00 starting from:

a) 1.00 M KH₂PO₄ and 1.00 M Na₂HPO₄


What I do know is that the pKa of H₂PO₄ is 6.82, and I was told this is the only pka necessary, but I don't know why the pka of HPO₄ is not necessary.

[Borek]

Solution is dominated by the H₂PO₄^- and its conjugated base, other acids/bases are present in minute quantities.

[Link The Worlds]

Okay, that makes sense. But what if instead of 1.00 M KH2PO4 and 1.00 M Na2HPO4, there is 1.2 M K₂HPO₄ and 2 M H₂SO₄.


When I plug H₂SO₄'s pka value (-3) into the Henderson-Hasselbech equation, I come out with A/HA = 1 x 10¹⁰

So I don't know what to do first.

[AWK]

Sulfuric acid is much stronger than phosphoric one, so calculate reaction between salt and sulfuric acid first.