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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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smokeyd smokeyd
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11 years ago
Dihydrogen phosphate H2PO4^- , has an acid dissociation constant of 6.2 x 10^-7. What is the conjugate base of H2PO4^- and what is its base dissociation constant?

A. H3PO4 , 1.6 x 10^6
B. H3PO4 , 1.6 x 10^-8
C. HPO4^2- , 1.6 x 10^6
D. HPO4^2- , 1.6 x 10^-8
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spa
wrote...
#1
11 years ago
Dihydrogen phosphate behaves as a Bronsted-Lowry acid in the following way:

H2PO4^- + H2O <-> HPO4^-2 + H3O^+

H2PO4^- is the acid, HPO4^-2 is the conjugate base.

To find Kb, use the relationship Ka x Kb = Kw.

Kw/Ka = Kb
 Kb = (10^-14) / (6.2x10^-7) = 1.61x10^-8

So, the correct answer is D.
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