key term - Stability of Conjugate Base

Definition

The stability of a conjugate base refers to how well it can exist in its anionic form after an acid donates a proton. A more stable conjugate base indicates that the corresponding acid is stronger because it is more willing to lose a proton. Factors such as electronegativity, resonance, and inductive effects play crucial roles in determining this stability.

5 Must Know Facts For Your Next Test

1. A strong acid has a weak conjugate base because it dissociates completely in solution.
2. The stability of the conjugate base can increase with higher electronegativity of the atom bearing the negative charge.
3. Resonance structures can greatly enhance the stability of a conjugate base, as they allow for delocalization of the negative charge.
4. Inductive effects from nearby electronegative atoms can stabilize a conjugate base by spreading out the negative charge.
5. The more stable the conjugate base, the more likely the corresponding acid will donate its proton, confirming the relationship between acid strength and base stability.

Review Questions

• How does resonance affect the stability of a conjugate base and subsequently influence acid strength?
  • Resonance allows for delocalization of electrons in a conjugate base, spreading out any negative charge over multiple atoms. This delocalization stabilizes the anion, making it less likely to re-accept a proton. As a result, acids that form resonance-stabilized conjugate bases are typically stronger, as they can donate protons more readily due to this increased stability.
• Compare the stability of conjugate bases formed from strong acids versus weak acids, and explain the significance in terms of Ka values.
  • Conjugate bases from strong acids are generally less stable than those from weak acids because strong acids dissociate completely in solution, leading to weaker conjugate bases. In terms of Ka values, strong acids have high Ka values indicating they readily donate protons, while their conjugate bases do not readily accept protons back. In contrast, weak acids have lower Ka values and their conjugate bases are more stable, making them less likely to donate protons.
• Evaluate how electronegativity and inductive effects contribute to the stability of a conjugate base and discuss their implications for predicting acid strength.
  • Electronegativity plays a crucial role in stabilizing conjugate bases; when the atom bearing the negative charge is more electronegative, it holds onto that charge more effectively, leading to increased stability. Inductive effects also come into play when electronegative atoms are present nearby, pulling electron density away from the negative charge and further stabilizing the anion. Together, these factors enable us to predict that acids with highly electronegative atoms or strong inductive effects will be stronger, as their corresponding conjugate bases are stabilized by these influences.

Related terms

Acid Strength: A measure of how readily an acid donates protons; stronger acids have more stable conjugate bases.

Ka:

The acid dissociation constant that quantifies the strength of an acid in solution; a larger Ka value indicates a stronger acid and a more stable conjugate base.

Resonance Stabilization: A phenomenon where a molecule can be represented by multiple valid Lewis structures, which contributes to the stability of the conjugate base.