As a technician in a large pharmaceutical research firm, you need to produce 450

Question

As a technician in a large pharmaceutical research firm, you need to produce 450. mL of a potassium dihydrogen phosphate buffer solution of pH = 6.78. The pKa of H_2PO^-_4 is 7.21. You have the following supplies: 2.00 L of 1.00 M KH_2PO_4 stock solution. 1.50L of 1.00 M K_2HPO_4 stock solution, and a carboy of pure distilled H_2O. How much 1.00 M KH_2PO_4 will you need to make this solution? (Assume additive volumes.) Express your answer to three significant digits with the appropriate units. Carbon dioxide (CO_2) and bicarbonate (HCO^-_3) concentrations in the bloodstream are physiologically controlled to keep blood pH constant at a normal value of 7.40. Physicians use the following modified form of the Henderson equation to track changes in blood pH

Explanation / Answer

pH = 6.78

pKa = 7.21

total volume of buffer = 450 mL

volume of KH2PO4 = x

volume of K2HPO4 = 450 - x

millimoles of KH2PO4 = x

millimoles of K2HPO4 = 450 - x

pH = pKa + log [salt / acid]

6.78 = 7.21 + log [450 - x / x ]

[450 - x / x ] = 0.3715

x = 328 mL

volume of KH2PO4 needed = 328 mL

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