What NEET Asks
- Numerical problems involving pH, pOH, and buffer solutions are very common, often carrying 4 marks.
- Conceptual questions on acid-base theories, common ion effect, and hydrolysis are frequently asked.
- Solubility product calculations, especially with common ion effect, are high-scoring.
Key Points
- Arrhenius Theory: Acids produce H⁺, bases produce OH⁻ in water.
- Brønsted-Lowry Theory: Acids are proton donors, bases are proton acceptors. Conjugate acid-base pairs differ by a proton.
- Lewis Theory: Acids are electron pair acceptors, bases are electron pair donors.
- pH Scale: Measures acidity/basicity; pH = -log[H⁺]. pH + pOH = 14 at 25°C.
- Buffer Solutions: Resist pH change upon small additions of acid or base; consist of a weak acid/its conjugate base or weak base/its conjugate acid.
- Common Ion Effect: Shifts equilibrium of a weak electrolyte on adding a strong electrolyte with a common ion, decreasing ionization.
- Hydrolysis: Reaction of ions of a salt with water, altering pH.
- Solubility Product (Ksp): Product of molar concentrations of ions in a saturated solution, each raised to its stoichiometric coefficient.
Must-Know Formula / Reaction
Henderson-Hasselbalch Equation (for acid buffers): pH = pKa + log([Salt]/[Acid])
- pH: Potential of Hydrogen
- pKa: -log(Ka), where Ka is acid dissociation constant
- [Salt]: Molar concentration of the conjugate base (salt)
- [Acid]: Molar concentration of the weak acid
Common Mistakes
- Students often confuse strong acids/bases with weak ones, applying incorrect formulas (e.g., assuming complete dissociation for weak electrolytes).
- Don't ignore the common ion effect in solubility problems or buffer calculations; it significantly impacts concentrations.
- Miscalculating the hydrolysis constant (Kh) or the degree of hydrolysis (h) for salt solutions, leading to incorrect pH values.
Rapid Revision
Ionic equilibrium covers acid-base definitions, pH, buffer action, hydrolysis of salts, and solubility product. Remember Henderson-Hasselbalch for buffers, Ksp principles for solubility, and the common ion effect's impact. Always distinguish between strong and weak electrolytes.