What is the conjugate acid of HCO3 2 A. HCO32- B. CO3- c H2CO3 D CO32- E. HCO3
The Correct Answer and Explanation is:
The correct answer is C. H₂CO₃.
To understand why, let us break this down using fundamental acid-base theory. The bicarbonate ion, HCO₃⁻, acts as a Brønsted-Lowry base because it can accept a proton (H⁺). When it does, it becomes its conjugate acid, which contains one more proton than the base itself. Adding a proton to HCO₃⁻ forms H₂CO₃, known as carbonic acid.
The conjugate acid–base relationship is defined by the addition or removal of one proton. In this context:
- Base: HCO₃⁻
- Conjugate acid: H₂CO₃
This behavior is central in buffer systems. The carbonic acid–bicarbonate buffer system, for example, helps regulate blood pH. Here, HCO₃⁻ can act either as a base or an acid depending on the environment, making it amphiprotic. However, when asked for the conjugate acid specifically, we consider the scenario in which HCO₃⁻ accepts a proton.
Let us now look at the distractors:
- A. HCO₃²⁻ is not chemically valid, as HCO₃⁻ does not easily lose another electron to become doubly negative.
- B. CO₃⁻ is not a standard species in acid-base chemistry.
- D. CO₃²⁻ is the conjugate base of HCO₃⁻, not its conjugate acid.
- E. HCO₃⁻ is the original species, not its own conjugate acid.
Therefore, the conjugate acid of HCO₃⁻ is H₂CO₃, formed by the addition of a single proton. This reaction is reversible and plays a key role in physiological pH regulation, particularly in respiratory and renal function.
