Equilibrium Review Notes

Equilibrium Mini-Review

• Understanding equilibrium problems often compares to attempting a complex maneuver (e.g., a triple axle).
• Emphasize the importance of practice and resilience.

Calculating pH of Solutions

1. Sodium Fluoride (NaF)

   • Concentration: 0.100 M
   • Calculation:
     • Kb for F⁻ = $10^{-10.82}$
     • Use formula $y = 1.23 imes 10^{-6}$ M
     • pOH = 5.91, therefore pH = 8.09

2. Ammonium Bromide (NH4Br)

   • Concentration: 0.100 M
   • Calculation:
     • Ka for NH₄⁺ = $10^{-9.25}$
     • Calculate x = $7.50 imes 10^{-6}$ M, yielding pH = 5.13

3. Barium Acetate (Ba(CH3COO)₂)

   • Concentration: 0.100 M
   • Calculation:
     • Kb for Ac⁻ = $10^{-9.25}$
     • Calculate y = $1.06 imes 10^{-5}$ M
     • pOH = 4.97, therefore pH = 9.03

Reactions of Cations with Water

• Cations with acidic protons (e.g., NH4⁺) will reduce solution pH.
• Metal cations generally lower pH when hydrated.
  • Example reactions:
  • $NH4^+ + H2O <br /> ightleftharpoons H3O^+ + NH3$
  • $Fe^{3+} + H2O <br /> ightleftharpoons H^+ + Fe(OH)^{2+}$
• The metal cation's charge and size impact acidity; smaller and highly charged cations are more acidic.
  • Na⁺ and Ca²⁺ do not significantly affect pH due to their neutral hydroxides in solution.

pH of Salt Solutions

1. NaNO₃

   • pH = 7.0 (neutral)

2. Ca(NO₃)₂

   • pH = 6.9 (neutral)

3. Zn(NO₃)₂

   • pH = 5.5 (acidic)

4. Al(NO₃)₃

   • pH = 3.5 (acidic)

Effect of Cations and Anions on pH

• Conjugate bases of strong acids do not alter pH.
• Conjugate bases of weak acids will raise pH, while conjugate acids of weak bases lower pH.

Salt and pH Predictions

• If neither cation nor anion reacts with water: pH ≈ neutral.
• If cation reacts but anion does not: pH < neutral.
• If anion reacts but cation does not: pH > neutral.
• If both react: pH determined by their respective Ka and Kb values.

Determining Acidic, Basic, or Neutral Properties of Salts

1. Ba(CH3COO)₂:

   • Basic (Ac⁻ hydrolyzes, produces OH⁻).

2. NH₄Cl:

   • Acidic (NH4⁺ contributes acidity).

3. CH₃NH₃Br:

   • Acidic (conjugate acid of a weak base).

4. KNO₃:

   • Neutral (neither ion reacts with water).

5. Al(ClO₄)₃:

   • Acidic (Al³⁺ contributes acidity).

Condition of Amphiprotic Salts

• Salts with polyprotic acids like NaHSO₃ can either lower or raise pH, depending on the action of their conjugates (e.g., HSO₃⁻).

Buffer Preparations and Calculations

• Buffers resist pH changes and consist of weak acid/base pairs.
• The effective pH range of a buffer is pKa ± 1.
• Henderson-Hasselbalch Equation:
  • pH = pKa + log rac{[A^-]}{[HA]}

Solubility Product (Ksp)

• Ksp denotes the equilibrium condition for the saturation state of ionic compounds:
  • Example: For $Hg2Cl2 <br /> ightleftharpoons Hg^{2+} + 2Cl^{-}, Ksp = [Hg^{2+}][Cl^-]^2$

Conclusion

• Prepare for complexities in equilibrium calculations similar to advanced sports maneuvers.
• Regular practice will enhance proficiency and understanding of these fundamental chemistry concepts.