Question

Identify conjugate acid and conjugate base for \( HCO_3^- \) ion respectively:

• A. Carbonic acid and carbonate ion
• B. Carbonate ion and carbonic acid
• C. Hydronium ion and hydroxide ion
• D. Water and carbon dioxide

Hint:

Remember: \[ \text{Conjugate Acid} = \text{Species} + H^+ \] \[ \text{Conjugate Base} = \text{Species} - H^+ \] Always carefully check the charge after adding or removing a proton.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The bicarbonate ion (\( HCO_3^- \)) is an amphiprotic species, meaning it can either donate a proton (act as an acid) or accept a proton (act as a base).
1. When a species accepts a proton (\( H^+ \)), it becomes its Conjugate Acid.
2. When a species donates a proton (\( H^+ \)), it becomes its Conjugate Base.
Step 2: Detailed Explanation:
Part A: Finding the Conjugate Acid
To find the conjugate acid, we add one \( H^+ \) ion to \( HCO_3^- \):
\[ HCO_3^- + H^+ \rightarrow H_2CO_3 \text{ (Carbonic acid)} \]
The charge changes from -1 to 0.

Part B: Finding the Conjugate Base
To find the conjugate base, we remove one \( H^+ \) ion from \( HCO_3^- \):
\[ HCO_3^- \rightarrow H^+ + CO_3^{2-} \text{ (Carbonate ion)} \]
The charge changes from -1 to -2.
Step 3: Final Answer Construction:
The question asks for the conjugate acid and base respectively.
Acid: \( H_2CO_3 \)
Base: \( CO_3^{2-} \)
Therefore, the correct pair is \( H_2CO_3 \) and \( CO_3^{2-} \).
Step 4: Final Conclusion:
This corresponds perfectly to option (D).