Part A Carbonic acid reacts with water to yield bicarbonate ions and hydronium ions: H2CO3 + H2O = HCO3¯ + H3O+ Identify the conjugate acid-base pairs. Drag each item to the appropriate bin. • View Available Hint(s) Reset Help H2O HCO3 H2CO3 H3O+ Acid Conjugate base Base Conjugate acid None Acids and bases have been defined in different ways. Arrhenius defined an acid as a compound that dissolves in water to increase the concentration of H+, and a base as a compound that increases the concentration of OH. Later, Brønsted and Lowry modified the definition: Acids are proton donors, and bases are proton acceptors. The Brønsted-Lowry definition of acids and bases is represented generically by this reaction, where HA is an acid and B is a base: HA + B = A + BH+ An acid that has lost a proton is that acid’s conjugate base (A). A base that has accepted a proton is that base’s conjugate acid (BH+). For each acid-base reaction, there are two conjugate acid-base pairs. The word conjugate is related to the word conjugal, which means “having to do with marriage.” A wife is only a wife to her husband, and a husband is only a husband to his wife. Similarly, a conjugate acid is defined as “conjugate” only in relation to the base from which it is derived, and a conjugate base is so defined only in relation to the acid from which it is derived. Conjugate acid-base pairs are identified as pairs because they are defined only in relation to each other. Part A Carbonic acid reacts with water to yield bicarbonate ions and hydronium ions: Identify the conjugate acid-base pairs. • View Available Hint(s) Acid H2O Conjugate base H2CO3 + H2O = HCO3 + H3O+ HCO3 H2CO3 H3O+ Base Conjugate acid I Reset Help
The Correct Answer and Explanation is:
Correct Categorization of Each Species
Acid:
- H₂CO₃ (carbonic acid)
Base:
- H₂O (water)
Conjugate Base:
- HCO₃⁻ (bicarbonate ion)
Conjugate Acid:
- H₃O⁺ (hydronium ion)
Explanation
In the reaction:
H₂CO₃ + H₂O ⇌ HCO₃⁻ + H₃O⁺
we are observing a Brønsted-Lowry acid-base reaction. According to this theory, acids are proton (H⁺) donors, and bases are proton acceptors. When identifying conjugate acid-base pairs, we look at the species that donate and accept protons and how they transform after the reaction.
Step-by-step breakdown:
- H₂CO₃ (carbonic acid) donates a proton (H⁺) to H₂O (water). Since it donates a proton, H₂CO₃ acts as the acid.
- After losing a proton, H₂CO₃ becomes HCO₃⁻ (bicarbonate ion). This species is now capable of accepting a proton in the reverse reaction, making it the conjugate base of H₂CO₃.
- H₂O accepts the proton donated by H₂CO₃, which classifies it as the base in this reaction.
- After gaining the proton, H₂O becomes H₃O⁺ (hydronium ion), which can donate a proton in the reverse reaction. Therefore, it is the conjugate acid of H₂O.
To summarize the conjugate acid-base pairs:
- H₂CO₃ / HCO₃⁻ → H₂CO₃ is the acid; HCO₃⁻ is its conjugate base.
- H₂O / H₃O⁺ → H₂O is the base; H₃O⁺ is its conjugate acid.
This reaction illustrates the reversible nature of acid-base reactions, where the acid and base react to form their conjugates. Each acid has a corresponding conjugate base, and each base has a conjugate acid. Understanding these pairs helps in identifying how substances will behave in acid-base reactions, especially in buffer systems like carbonic acid in the blood.
