Question

use the following information to answer the next question.
carbonic acid, h₂co₃(aq), is a chemical substance which
plays an important role in controlling the ph of body fluids.
in aqueous solution it produces hco₃⁻(aq) and co₃²⁻(aq)
as shown below:
h₂co₃(aq) + h₂o(ℓ) → h₃o⁺(aq) + hco₃⁻(aq)
hco₃⁻(aq) + h₂o(ℓ) → h₃o⁺(aq) + co₃²⁻(aq)

in the above equilibrium reactions, h₂co₃(aq) is a(n)
○ strong acid
○ amphiprotic substance
○ polyprotic acid
○ polyprotic base
○ strong base

Explanation:

1. Analyze each option:

• Strong acid: Strong acids dissociate completely in solution. \( \ce{H2CO3} \) does not dissociate completely (it has two successive equilibria), so it's not a strong acid.
• Amphiprotic substance: An amphiprotic substance can act as both an acid and a base (donate and accept \( \ce{H+} \)). \( \ce{H2CO3} \) only donates \( \ce{H+} \) (in the given reactions), so it's not amphiprotic.
• Polyprotic acid: A polyprotic acid donates more than one proton (\( \ce{H+} \)) per molecule in successive steps. \( \ce{H2CO3} \) donates one \( \ce{H+} \) to form \( \ce{HCO3-} \) and then another \( \ce{H+} \) from \( \ce{HCO3-} \) to form \( \ce{CO3^{2-}} \), so it donates two protons overall, making it a polyprotic acid.
• Polyprotic base: A polyprotic base accepts more than one proton. \( \ce{H2CO3} \) donates protons, not accepts, so it's not a polyprotic base.
• Strong base: Strong bases are hydroxides or substances that dissociate completely to give \( \ce{OH-} \). \( \ce{H2CO3} \) is an acid, not a base.

Answer:

polyprotic acid (the option with "polyprotic acid" text)