Course Code: CHM-DSC-251
Paper Name: Physical Chemistry - II
Ionic equilibrium involves the equilibrium between unionized molecules and ions in solution.
The fraction of the total number of molecules of an electrolyte that ionizes in solution. It is affected by:
Water is a very weak electrolyte that undergoes self-ionization.
Kw = [H+][OH-] = 1.0 x 10^-14 (at 298 K)
A logarithmic scale used to specify the acidity or basicity of an aqueous solution.
pH = -log [H+]
At 298 K: pH + pOH = 14.
Salt hydrolysis is the reaction of an anion or cation of a salt with water to produce acidity or alkalinity.
| Salt Type | Nature of Solution | Example |
|---|---|---|
| Strong Acid + Strong Base | Neutral (pH = 7) | NaCl, KNO3 |
| Weak Acid + Strong Base | Alkaline (pH > 7) | CH3COONa |
| Strong Acid + Weak Base | Acidic (pH < 7) | NH4Cl |
| Weak Acid + Weak Base | Depends on Ka/Kb | CH3COONH4 |
A buffer solution resists changes in pH when small amounts of acid or base are added.
Used to calculate the pH of a buffer solution.
pH = pKa + log ([Salt] / [Acid])
Titration curves show the change in pH as a titrant is added.
Weak organic acids or bases that change color within a specific pH range.
Q: What is the buffer capacity?
A: It is a measure of the effectiveness of a buffer in resisting pH changes.
Q: Define Salt Hydrolysis.
A: It is the interaction of salt ions with water, leading to an excess of H+ or OH- ions.
Q: Why does NH4Cl give an acidic solution?
A: NH4+ ions undergo hydrolysis to produce H3O+ ions, making the solution acidic.