By John Brennan • Updated Aug 30, 2022

When chemists need to determine the concentration of a dissolved species, they typically employ titration. By adding a reagent that reacts quantitatively with the analyte until the reaction reaches the equivalence point, the chemist can back‑calculate the original concentration.

Step 1: Identify Acid or Base Strength

Determine whether the analyte and titrant are strong or weak. A strong acid fully donates protons; a strong base fully accepts them. Common strong acids include HCl, HNO₃, H₂SO₄, HClO₄, HBr, and HI. Strong bases include LiOH, NaOH, KOH, RbOH, Ca(OH)₂, Sr(OH)₂, and Ba(OH)₂. See the full list of common acids and bases.

Step 2: Predict the Salt’s Nature

When a strong acid reacts with a strong base, the resulting salt is neutral (pH ≈ 7). A strong acid with a weak base gives an acidic salt; a strong base with a weak acid yields a basic salt. Titrations rarely pair two weak species because locating the equivalence point becomes challenging.

Step 3: Clarify the Problem Statement

List the known quantities: identities of analyte and titrant, analyte volume, titrant concentration, and any given moles or volumes at equivalence. Decide what the question asks—whether it’s the concentration of the analyte, the pH at a particular stage, or the pH at equivalence.

Step 4: Write the Balanced Equation

Write the stoichiometric equation for the acid–base reaction. Use it to determine the molar ratio between reactants, which will be needed when converting moles to concentration.

Step 5: Calculate pH at Desired Points

Depending on the acid/base strengths, use one of the following approaches:

• Strong acid ↔ strong base – pH = –log[acid]. Subtract moles of titrant added, divide by total volume.
• Strong base ↔ strong acid – Follow the same steps, but compute pOH first: pOH = –log[base]. Convert to pH by pH = 14 – pOH.
• Weak acid ↔ strong base – Apply the Henderson–Hasselbalch equation: pH = pKₐ + log([A⁻]/[HA]). The concentration of the conjugate base equals the moles of titrant added divided by total volume.
• Weak base ↔ strong acid – Use the conjugate form: pOH = pK_b + log([BH⁺]/[B]), then convert to pH.

For the pKₐ values of common weak acids, see the reference table.

Step 6: Find the pH at Equivalence

• Strong acid + strong base – pH ≈ 7.

• Strong acid + weak base – Calculate the concentration of the conjugate base at equivalence, take –log to obtain pOH, then convert to pH.

• Strong base + weak acid – Same procedure, but start from pOH and convert to pH.

Step 7: Determine the Original Concentration of the Analyte

Multiply the volume of titrant added to reach equivalence by its molarity to obtain moles of titrant. Multiply by the stoichiometric ratio from Step 4 to find moles of analyte initially present. Divide by the initial analyte volume to get its concentration.

TL;DR

Assume a 1:1 stoichiometry for most general‑chemistry titrations, and follow the steps above to solve any problem.

Warning

Always include the volume of titrant added when computing concentrations before or at the equivalence point.