Acid–Base TitrationJEE Main

Concept

A titration tracks pH as base is added to acid. The curve stays gentle, then leaps at the equivalence point — where moles of base exactly neutralise the acid. A weak acid adds a flat buffer region before the jump.

Key formula

Derivation

Before equivalence the leftover strong acid sets $[H^+] = \dfrac{n_{acid}-n_{base}}{V_{total}}$. For a weak acid the buffer region follows Henderson–Hasselbalch, with pH = p$K_a$ at the half-equivalence point.

At equivalence a strong–strong titration gives pH 7; a weak acid leaves its conjugate base, which hydrolyses to give pH > 7. Past equivalence, excess $OH^-$ dominates.

Scenarios to explore

• Acid–Base Titration — pH curve and the equivalence point.

Real-world applications

• Determining unknown acid concentrations in the lab.
• Choosing indicators (matched to the equivalence pH).
• Quality control of foods and pharmaceuticals.

JEE exam tips

• Half-equivalence (Vb = Veq/2) of a weak acid gives pH = p$K_a$ directly.
• Equivalence volume is $V_{eq} = C_aV_a/C_b$ regardless of strength.

Common mistakes

• Assuming every equivalence point is at pH 7 — only strong–strong is.
• Forgetting the total volume increases as titrant is added.
• Mislabelling the half-equivalence point — that is where pH = p$K_a$.

Exam traps to avoid

• A weak-acid equivalence point is basic (pH > 7) due to conjugate-base hydrolysis.
• The steep region is narrow for strong acids, broader/lower for weak ones.