Acid and base strength describes how readily a substance donates or accepts protons ($H^+$). Strong acids and bases completely dissociate in water, while weak acids and bases only partially dissociate. The strength of an acid is quantified by its acid dissociation constant, $K_a$, and the strength of a base is quantified by its base dissociation constant, $K_b$. A larger $K_a$ indicates a stronger acid, and a larger $K_b$ indicates a stronger base. Understanding these concepts is crucial for predicting the direction of reactions and calculating pH.
Factors affecting acid strength include the electronegativity of the atom bonded to the acidic proton and the stability of the conjugate base. For example, in hydrohalic acids (HF, HCl, HBr, HI), acidity increases down the group due to increasing bond length and decreasing bond strength. Similarly, resonance stabilization of the conjugate base increases acidity.
Match the following terms with their definitions:
| Term | Definition |
|---|---|
| 1. Strong Acid | A. A substance that accepts protons. |
| 2. Weak Base | B. An acid that completely dissociates in water. |
| 3. $K_a$ | C. A base that only partially dissociates in water. |
| 4. Conjugate Base | D. The equilibrium constant for the dissociation of an acid. |
| 5. Bronsted-Lowry Base | E. The species remaining after an acid has donated a proton. |
Complete the following paragraph using the words: dissociation, $K_b$, strong, weak, conjugate.
A _______ acid undergoes complete _______ in water, while a _______ acid only partially dissociates. The strength of a base is measured by its _______ value. The species formed when an acid donates a proton is called its _______ base.
Explain how the structure of a molecule affects its acid strength. Provide specific examples to support your answer.
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