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Standard 4-Mark Question in NEB Chemistry Board ExamsClass 12 • Chemistry • Unit 2

Rating: 5 / 5

Defensible Pedagogical Basis:

Specification Grid Section 1 (Physical Chemistry): Buffer solutions and the Henderson-Hasselbalch equation are compulsory numerical and derivation items in NEB Group B.

Approach Summary: Set up equilibrium HA ⇌ H⁺ + A⁻ with Ka = [H⁺][A⁻]/[HA]. Take negative logarithm to obtain pH = pKa + log([A⁻]/[HA]). Explain why [A⁻] ≈ [Salt] and [HA] ≈ [Acid] due to common ion effect.

Open Chapter Unit 2 Notes →