Which of the following has the strongest conjugate base? A. O cyanic acid, K = 3.510^4 B. O chlorous acid, K = 1.110^-1 C. O hypobromous acid, K = 2.810^-9 D. O acetic acid, K = 1.810^-5
The Correct Answer and Explanation is:
The strength of a conjugate base is inversely related to the strength of its parent acid. In other words, the stronger the acid, the weaker its conjugate base, and vice versa. To determine which has the strongest conjugate base, we need to look at the acid dissociation constant (Ka) for each acid. A stronger acid has a larger Ka value, indicating that it dissociates more in solution, leading to a weaker conjugate base.
Given the acid dissociation constants for each acid:
- A. Cyanic acid, Ka = 3.5 × 10⁴
- B. Chlorous acid, Ka = 1.1 × 10⁻¹
- C. Hypobromous acid, Ka = 2.8 × 10⁻⁹
- D. Acetic acid, Ka = 1.8 × 10⁻⁵
The acid with the smallest Ka value will have the strongest conjugate base, since weaker acids produce stronger conjugate bases.
Let’s examine the values:
- Cyanic acid has the largest Ka (3.5 × 10⁴), meaning it is the strongest acid, and thus, its conjugate base is the weakest.
- Chlorous acid has a moderate Ka value (1.1 × 10⁻¹), meaning it’s a stronger acid than acetic and hypobromous acids, but weaker than cyanic acid.
- Hypobromous acid has the smallest Ka value (2.8 × 10⁻⁹), indicating it is the weakest acid of the list, making its conjugate base the strongest.
- Acetic acid has a Ka value of 1.8 × 10⁻⁵, which makes it stronger than hypobromous acid but weaker than chlorous acid.
Thus, C. Hypobromous acid has the weakest acid strength, and its conjugate base is the strongest. This is because weak acids have stronger conjugate bases.
Correct Answer: C. Hypobromous acid
