Ionic Equilibrium and pH Calculation

Introduction

• Some species can behave like conjugate acids and bases.
• How to calculate pH of a weak monobasic acid.

Formula

• Formula for pH:
  • (\text{pH} = -\log[\text{H}^+])
• Minus log formula, such as to find pH (\text{pH} = -\log[\text{H}^+])
• To find pK(_a) (\text{pK}_a = -\log[\text{K}a])

Ionic Equilibrium

• Ionic equilibrium occurs where ions are involved.
• Strong and weak electrolytes:
  • Strong electrolytes completely dissociate into their ions.
  • Weak electrolytes partially ionize.
• Equilibrium constant is high for strong electrolytes.

Types of Electrolytes

• Strong electrolytes:
  • Strong acids, strong bases, and salts.
• Weak electrolytes:
  • Weak acids and weak bases.
  • Organic acids are weak.

Acid-Base Theory

• Arrhenius Theory:
  • Acid: donates (\text{H}^+) ions.
  • Base: donates (\text{OH}^-) ions.
• Bronsted-Lowry Concept:
  • Acid: donates (\text{H}^+).
  • Base: accepts (\text{H}^+).

Conjugate Acid-Base Pairs

• Acids and bases that can convert into each other.
• (\text{H}2\text{O} \leftrightarrow \text{OH}^- + \text{H}^+)

Lewis Acid-Base Concept

• Lewis Acid: electron pair acceptors.
• Lewis Base: electron pair donors.

Weak Electrolytes and Ionic Product

• The ionization constant of weak electrolytes is determined by (\text{K}_a).
• Ionic product of water (\text{K}_w = 10^{-14})

pH and pOH

• (\text{pH} = -\log[\text{H}^+])
• (\text{pOH} = -\log[\text{OH}^-])
• In a neutral solution (\text{pH} = 7) at 25 degrees Celsius

Calculating pH in a Mixture

• pH calculation:
  • In solutions with strong acids/bases, (\text{pH} \neq 7)
  • For weak acids/bases (\text{pH} = \text{pK}a - \log\frac{\text{moles of acid}}{\text{moles of base}})

Salt Hydrolysis

• Understanding salt hydrolysis when acid and base meet.
• Cationic and anionic hydrolysis.

Buffer Solutions

• Buffer solutions resist large changes in pH.
• Acidic buffer: mixture of a weak acid and its salt.
• Basic buffer: mixture of a weak base and its salt.

Solubility and Solubility Product

• Relationship between solubility product (\text{K}_\text{SP}) and solubility (\text{S}).
• (S^n = \text{K}_\text{SP})

Common Ion Effect

• Solubility decreases in the presence of a common ion.
• (\text{Common ion effect: reduces solubility}).

Odd Ion Effect

• Presence of an odd ion can increase solubility.

These notes cover key points of ionic equilibrium and pH calculation. By reading these notes, you can understand the relationship between weak and strong acids-bases, conjugate pairs, buffer solutions, and solubility products.