Identify the conjugate base for each acid. conjugate base of
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The Correct Answer and Explanation is:
The conjugate base of H₂S is HS⁻.
When identifying a conjugate base, we follow the principle that a conjugate base forms when an acid donates a proton (H⁺). This idea comes from the Bronsted-Lowry theory, which defines acids as proton donors and bases as proton acceptors.
Hydrosulfuric acid (H₂S) is a weak diprotic acid, meaning it can donate two protons, but it does so step by step. The first deprotonation involves H₂S donating one proton to produce the hydrosulfide ion (HS⁻):
H₂S → H⁺ + HS⁻
Here, H₂S acts as the acid because it donates a proton, and HS⁻ is its conjugate base—the species remaining after the loss of a proton. This conjugate base is capable of accepting a proton again, returning to H₂S under suitable conditions.
Conceptually, the acid and its conjugate base form a pair that is linked by the gain or loss of a single hydrogen ion. The stronger the acid, the weaker its conjugate base, and the weaker the acid, the stronger its conjugate base. Since H₂S is a weak acid, HS⁻ is considered a relatively strong conjugate base by comparison, although not among the strongest bases overall.
Understanding conjugate pairs helps in predicting reaction directions, analyzing buffer systems, and calculating equilibrium constants. In buffer solutions, weak acids and their conjugate bases work together to resist drastic changes in pH. For instance, if HS⁻ is present in solution, it can help moderate acidity by accepting excess protons.
To summarize: the conjugate base of H₂S is HS⁻, created when the acid donates one hydrogen ion. This transformation reflects the foundational ideas in acid-base chemistry and highlights the reversible nature of proton transfer reactions.
