I need some help been stuck on this one for 20 mins Part A As a technician in a
ID: 508240 • Letter: I
Question
I need some help been stuck on this one for 20 mins
Part A
As a technician in a large pharmaceutical research firm, you need to produce 450. mL of a potassium dihydrogen phosphate buffer solution of pH = 7.07. The pKa of H2PO4 is 7.21.
You have the following supplies: 2.00 L of 1.00 M KH2PO4 stock solution, 1.50 L of 1.00 M K2HPO4 stock solution, and a carboy of pure distilled H2O.
How much 1.00 M KH2PO4 will you need to make this solution? (Assume additive volumes.)
Express your answer to three significant digits with the appropriate units.
Volume of KH2PO4 needed =
Explanation / Answer
total volume of buffer = 450 mL
volume of KH2PO4 = x mL
volume of K2HPO4 = 450 - x mL
pH = pKa + log [K2HPO4 / KH2PO4]
7.07 = 7.21 + log [K2HPO4 / KH2PO4]
[K2HPO4 / KH2PO4] = 0.7244
[ x / 450 - x ] = 0.7244
x = 189. mL
volume of KH2PO4 = 189 mL