Textbook Question
Write balanced net ionic equations and the corresponding equilibrium equations for the stepwise dissociation of the triprotic acid H3PO4.
334
views
17. Acid and Base Equilibrium
Triprotic Acids and Bases
Multiple Choice
Which sequence of chemical equations correctly represents the stepwise ionization of the triprotic acid H3PO4 in water?
A
H3PO4 + H2O → PO4^{3-} + 3H3O^+
B
H3PO4 + H2O → H2PO4^- + H3O^+; H2PO4^- + H2O → HPO4^{2-} + H3O^+; HPO4^{2-} + H2O → PO4^{3-} + H3O^+
C
H3PO4 + 3H2O → PO4^{3-} + 3H3O^+
D
H3PO4 → H2PO4^- + H^+; H2PO4^- → HPO4^{2-} + H^+; HPO4^{2-} → PO4^{3-} + H^+
Verified step by step guidance1
Understand that a triprotic acid like H3PO4 can lose three protons (H⁺) stepwise, each step representing one ionization equilibrium.
Write the first ionization step where H3PO4 donates one proton to water, forming the dihydrogen phosphate ion (H2PO4⁻) and hydronium ion (H3O⁺):
\[H\3PO\4 + H\2O \rightarrow H\2PO\4^- + H\3O^+\]
Write the second ionization step where H2PO4⁻ donates a proton to water, forming the hydrogen phosphate ion (HPO4^{2-}) and another hydronium ion:
\[H\2PO\4^- + H\2O \rightarrow HPO\4^{2-} + H\3O^+\]
Write the third ionization step where HPO4^{2-} donates the last proton to water, forming the phosphate ion (PO4^{3-}) and a hydronium ion:
\[HPO\4^{2-} + H\2O \rightarrow PO\4^{3-} + H\3O^+\]
Note that each step involves water acting as a base accepting a proton, and the acid species losing one proton at a time, which is characteristic of stepwise ionization of polyprotic acids.
Related Videos
Related Practice
