Using stocks of 0.1 M KH2PO4 and 0.1 M K2HPO4 how much 0.1 M K2HPO4 is needed to prepare 20 mL of a buffer solution at pH 7.2. The pKa of phosphate is 6.82.

Question

I know to solve for the ratio using henderson hasselbach but im lots after that!

5.2=6.82+log(A/HA)
1.0024HA=A

Answer 1

I think you need the total concentration of the buffer; i.e., you want 20 mL of what? 0.05M, 0.01M, what M. Here is a problem just like that which I worked earlier last week.
http://www.jiskha.com/display.cgi?id=1470250931