- #1

Winback

- 1

- 0

## Homework Statement

As a technician in a large pharmaceutical research firm, you need to produce 100.0 mL of 1.00 M potassium phosphate buffer solution of pH = 7.14. 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?

C(a) represents the volume of the conjugate acid (in milliliters), and C(b) represents the volume of the conjugate base (in milliliters).

## Homework Equations

C(a) + C(b) = 100.0 mL

C(b) / C(a) = calculated ratio (0.85)

C(b) = C(a) x calculated ratio (0.85)

C(a) + ( C(a) x (0.85) ) = 100.0 mL

C(a) = 100.0 / (1+(0.85)) mL

## The Attempt at a Solution

I just for the life of me can't understand the section after the base/acid ratio is found.

7.14 = 7.21 + log [base]/[acid]

7.14 = 7.21 + log x

logx = pH - pKa (-.07)

x = 0.85 [base]/[acid] ratio

But after that I just honestly have no idea, I did a similar problem in class today but I just can't understand it now. I just would like to know what values belong where in the C(a) and C(b) equations and how to get those numbers so I can solve it myself. Thanks.

Last edited: