Recall that the conjugate acid of a base is simply the compound formed when a base gains a hydronium ion (H+). It's considered as an acid because it can lose H+ to reform the base.
On the other hand, the conjugate base of an acid is simply the compound formed when an acid loses a hydronium ion (H+). It's considered as a base because it can gain H+ to reform the acid.
Phosphoric acid (H3PO4) is a weak triprotic acid, meaning it can donate three protons (H+) and it will have three equilibrium reactions.
Removing one H+ per step in H3PO4:
H2PO4– is the conjugate _____ of H3PO4 and the conjugate _____ of HPO42–.
A. acid / acid
B. acid / base
C. base / acid
D. base / base
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