Homework Help: chemistry

Posted by teja on Friday, May 11, 2012 at 7:09am.

As a technician in a large pharmaceutical research firm, you need to produce 200 mL of 1.00 M a phosphate buffer solution of pH = 7.06. The pKa of H_2PO_4}^- is 7.21. You have 2.00 L of 1.00 M KH_2PO_4 solution and 1.50 L of 1.00 M K_2HPO_4 solution, as well as a carboy of pure distilled H_2O.

How much 1.00 M KH_2PO_4 will you need to make this solution?

chemistry - DrBob222, Friday, May 11, 2012 at 3:29pm
Use the Henderson-Hasselbalch equation and solve for (base)/(acid) ratio (this is equation 1).
The problem gives you equation 2 which is
(acid) + (base) = 1M

Solve these two equations simultaneously to determine mols acid and mols base needed; then translate this into volume of the two materials at hand. Post your work if you get stuck. I zipped through this very quickly and it appears you will need about 117 mL acid and about 83 mL of the base but I could have made a math error easily. You should confirm those numbers. .

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