Question

What is the conjugate base of \( OH^- \)?

• A. \( H_2O \)
• B. \( O^{2-} \)
• C. \( H_3O^+ \)
• D. \( H^+ \)

Hint:

Always consider the common ion forms and typical reactions in acid-base chemistry. \( OH^- \) as a base usually comes from water, which is its conjugate acid.

Answer 1

The Correct Option is B

Understanding Conjugate Acids and Bases: In Brønsted-Lowry acid-base theory, a conjugate base is formed by the removal of a proton (H$^+$) from an acid. Since \({OH}^-\) is itself a base, we need to determine what would form if it were to lose a proton. 
Step 1: Analyze the Possibility of OH$^-$ Losing a Proton. OH$^-$ losing a proton (which it doesn't possess in excess) would theoretically produce \({O}^{2-}\). 
Step 2: Correct Misconception. However, \( OH^- \) is typically the conjugate base of \( H_2O \). When \( H_2O \) acts as an acid and donates a proton, \( OH^- \) is what remains. Therefore, asking for the conjugate base of \( OH^- \) might seem unconventional, as \( OH^- \) is already a base. But in this context, further loss of a proton would indeed lead to \( O^{2-} \), though this is a highly theoretical and not commonly observed scenario.