The H 2 PO 4 - & HPO 4 2- combination plays a role in maintaining the pH of bloo

Question

The H2PO4- & HPO4 2- combination plays a role in maintaining the pH of blood.

Part A

Write equations to show how a solution containing these ions functions as a buffer when acid is added. Express your answer as a chemical ion equation.

Part B

Write equations to show how a solution containing these ions functions as a buffer when base is added. Express your answer as a chemical ion equation.

Part C

Calculate the pH when this buffer is most effective. Express your answer using one decimal place.

Part D

Calculate the pH of a buffer solution in which [H2PO4]= 0.043 M and [HPO42]= 0.174 M . [Hint: Focus on the second step of the phosphoric acid ionization.] Express your answer using two decimal places.

Explanation / Answer

A )

when acid is added to this buffer HPO4-2 ion react with acid form H2PO4-

HPO4-2 + H+ --------------------> H2PO4-

B)

when base is added to this buffer H2PO4- react with base forms HPO4-2

H2PO4- + OH- ------------------> HPO4- + H2O

C)

when   pH = pKa . the buffer is most efficient

pKa of this buffer = 7.20

so

pH = 7.2

D)

pH = pKa + log [HPO42] / [H2PO4]

pH = 7.20 + log (0.174 / 0.043)

pH = 7.81

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