Acid–Base Titration Calculator

Q: What about polyprotic acids/bases?

This version assumes monoprotic systems. Polyprotic titrations add more equivalence points and require extended handling.

Determine the pH at any titration stage for strong/weak acids and strong/weak bases. Supports SA+SB, SB+SA, WA+SB, and WB+SA with region-aware formulas (buffer, equivalence, excess). Clear steps included.

Background

We do mole bookkeeping, identify the titration region, and apply the appropriate model: strong excess (direct [H⁺] or [OH⁻]), buffer (Henderson–Hasselbalch), equivalence (hydrolysis of the conjugate). Assumes 25 °C: pH + pOH = 14.00, K_w = 1.0×10⁻¹⁴.

Select titration type and enter values:

Titration Type:

Initial Volume of Analyte (mL):

Analyte Concentration (M):

Titrant Concentration (M):

Volume of Titrant Added (mL):

Ka (if weak acid):

Not required for strong–strong. For WA+SB, enter Ka. For WB+SA, enter Kb.

Quick picks:

Result:

No results yet. Select a type and enter values.

How to use this calculator

Pick the titration type. The Ka/Kb field switches automatically.
Enter analyte volume (mL) and concentration (M).
Enter titrant concentration and the volume added (mL).
Click Calculate. We identify the region and apply the correct formula.

Assumes 25 °C (pH + pOH = 14.00). Uses Henderson–Hasselbalch for buffer regions and hydrolysis at equivalence for weak systems.

Formula & Equation Used

Strong excess: [H⁺] = n_excess/V_tot or [OH⁻] = n_excess/V_tot
Buffer (WA+SB): pH = pK_a + log([A⁻]/[HA])
Buffer (WB+SA): pOH = pK_b + log([BH⁺]/[B]); pH = 14 − pOH
Equivalence (WA+SB): [OH⁻] ≈ √(K_b·C_A⁻), K_b = K_w/K_a
Equivalence (WB+SA): [H⁺] ≈ √(K_a·C_BH⁺), K_a = K_w/K_b

Example Problem & Step-by-Step Solution

Example (WA + SB, pre-equivalence buffer)

25.0 mL 0.100 M acetic acid (Ka=1.8×10⁻⁵) + 12.5 mL 0.100 M NaOH.

n(HA)=0.00250 mol; n(OH⁻)=0.00125 mol ⇒ buffer: HA left, A⁻ formed.
pH = pK_a + log(n(A⁻)/n(HA left)) = 4.74 + log(0.00125/0.00125) = 4.74.
Using concentrations gives the same ratio because both are divided by V_tot.

Frequently Asked Questions

Q: Do I need Ka or Kb?

Only for weak systems: WA+SB needs Ka; WB+SA needs Kb. Strong–strong does not need either.

Q: Why can I use moles in Henderson–Hasselbalch?

Because both acid and base are in the same solution; dividing by the same volume cancels in the ratio.

Q: What about polyprotic acids/bases?

This version assumes monoprotic systems. For polyprotic titrations, additional equivalence points appear—coming soon.

Titrations: Weak Acid-Strong Base