As a technician in a large pharmaceutical research firm, you need to produce 100

Question

As a technician in a large pharmaceutical research firm, you need to produce 100. mL of 1.00 M potassium phosphate buffer solution of pH = 6.95. 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?

If the normal physiological concentration of HCO3 is 24 mM, what is the pH of blood if PCO2 drops to 26.0 mmHg ? Express your answer numerically using two decimal places.

Explanation / Answer

Using Hendersen-Hasselbalck equation,

pH = pKa + log([base]/[acid])

6.95 = 7.21 + log([HPO4^2-]/[H2PO4-])

[HPO4^2-] = 0.55[H2PO4-]

[H2PO4-] + [HPO4^2-] = 1 M x 0.1 L

[H2PO4-] + 0.55[H2PO4-] = 0.1

[H2PO4-] = 0.0645 mols = 0.0645/0.1 = 0.645 M

[HPO4^2-] = 0.0355 mols = 0.0355/0.1 = 0.355 M

Amount of KH2PO4 needed = 0.645 x 100/1 = 64.5 ml

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