Titration Curves - MCAT | Premier MCAT Prep

Titration Curves

13 min read Updated Mar 26, 2026

A titration curve is a graph of pH versus the volume of titrant (acid or base) added. It tells you everything: the strength of the acid or base being titrated, the pKa, the equivalence point, and the buffer region. Reading titration curves quickly is one of the most tested skills in MCAT general chemistry.

The Anatomy of a Titration Curve

Every titration curve has these regions:

Initial point - pH before any titrant is added
Buffer region - the gradual rise (or fall) where both HA and A⁻ coexist
Half-equivalence point - exactly halfway to the equivalence point, where [HA] = [A⁻] and pH = pKa
Equivalence point - where moles of acid = moles of base (neutralization complete)
Post-equivalence region - excess titrant dominates the pH

Strong Acid + Strong Base Titration

Example: Titrating HCl with NaOH

Key features:

Initial pH: low (determined by [HCl])
Equivalence point pH: exactly 7.0 (only water and a neutral salt remain)
Curve shape: steep, dramatic jump centered at pH 7
No buffer region (strong acids have no conjugate base that buffers)

At the equivalence point: moles HCl = moles NaOH. The solution contains only NaCl and water - both neutral.

Weak Acid + Strong Base Titration

Example: Titrating CH₃COOH with NaOH

Key features:

Initial pH: higher than the strong acid case (weak acid, less H⁺)
Buffer region: the flat area before the equivalence point where both CH₃COOH and CH₃COO⁻ coexist
Half-equivalence point: pH = pKa (this is how you find pKa experimentally)
Equivalence point pH: above 7 (the solution contains only the conjugate base CH₃COO⁻, which is a weak base)
Curve shape: gentler rise, equivalence point shifted above pH 7

Titration curve of a weak acid with a strong base showing initial point, before equivalence, equivalence point, and after equivalence regions — Titration curve of a weak acid titrated with a strong base. The four labeled regions show: the initial point (low pH), the buffer region before equivalence, the equivalence point (above pH 7 because the conjugate base is basic), and the post-equivalence region where excess strong base dominates. Source: Wikimedia Commons.

Weak Base + Strong Acid Titration

Example: Titrating NH₃ with HCl

Key features:

Initial pH: above 7 (basic solution)
Buffer region: where both NH₃ and NH₄⁺ coexist
Half-equivalence point: pOH = pKb, so pH = 14 - pKb = pKa of the conjugate acid
Equivalence point pH: below 7 (the solution contains NH₄⁺, a weak acid)
Curve shape: pH decreases as acid is added, steep drop at equivalence

Summary: Equivalence Point pH

Titration Type	Equivalence Point pH	Why
Strong acid + strong base	Exactly 7	Only neutral salt remains
Weak acid + strong base	Above 7	Conjugate base of weak acid remains (basic)
Weak base + strong acid	Below 7	Conjugate acid of weak base remains (acidic)
Weak acid + weak base	Depends on Ka vs. Kb	Compare Ka of conjugate acid to Kb of conjugate base

A pipette dispensing pink indicator solution into a multi-well plate in a chemistry laboratory — Acid-base chemistry in the lab. A pipette dispenses pink indicator solution into wells of a microplate. Color changes like this signal when a reaction endpoint has been reached. Source: Unsplash.

Overlaid titration curves comparing the titration of a strong acid HCl and a weak acid acetic acid with sodium hydroxide NaOH, showing the different equivalence point pH values and the buffer region present only for the weak acid — Titration curves for HCl (strong acid, blue) and acetic acid (weak acid, red) titrated with NaOH. Key differences: the weak acid starts at a higher pH, shows a buffer region before the equivalence point, and has an equivalence point above pH 7 due to hydrolysis of the conjugate base. *Credit: Wikimedia Commons, Public Domain*

Reading a Titration Curve on the MCAT

When you see a titration curve, extract this information immediately:

Initial pH - read from the y-axis at volume = 0
Equivalence point - the steepest part of the curve (the inflection point of the steep rise)
Volume at equivalence - read from the x-axis at the equivalence point
Half-equivalence volume - half of the equivalence volume
pH at half-equivalence - this equals pKa (for weak acid titrated with strong base)
pH at equivalence - above 7 (weak acid) or below 7 (weak base) or exactly 7 (strong-strong)

Calculating the Equivalence Point

At the equivalence point:

moles of acid = moles of base
$M_{\text{acid}}$ x $V_{\text{acid}}$ = $M_{\text{base}}$ x $V_{\text{base}}$ (for monoprotic acids and monobasic bases)

Solve for the unknown concentration or volume.

pH at the Equivalence Point of a Weak Acid Titration

At the equivalence point of a weak acid-strong base titration, all the HA has been converted to A⁻. The solution is equivalent to a solution of the sodium salt of the weak acid.

To find the pH: treat A⁻ as a weak base with Kb = Kw/Ka, and use [OH⁻] = √(Kb x c), where c is the concentration of A⁻ at the equivalence point (accounting for dilution).

A weak acid is titrated with NaOH. The equivalence point occurs at 25.0 mL of NaOH, and the pH at 12.5 mL of NaOH is 4.74. What is the pKa of the acid?

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pKa = 4.74. 12.5 mL is exactly half of 25.0 mL (the equivalence volume), so 12.5 mL is the half-equivalence point. At the half-equivalence point, [HA] = [A⁻], so pH = pKa. The acid is acetic acid (pKa = 4.74).

Is the equivalence point pH of a weak base titrated with a strong acid above 7, below 7, or exactly 7?

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Below 7 (acidic). At the equivalence point, all of the weak base has been converted to its conjugate acid. The conjugate acid of a weak base is itself a weak acid, which will donate protons to water and make the solution acidic. For example, titrating NH₃ with HCl produces NH₄⁺ at equivalence - a weak acid with

K_a = 5.6 \times 10^{-10}