Acid-Base Titration Calculator
Calculate the concentration, volume, or moles of acid or base in a titration.
Solve for unknown concentration using the titration equation and equivalence point data.
What Is a Titration?
An acid-base titration is a quantitative analytical technique used to determine the concentration of an unknown acid or base (the analyte) by reacting it with a standard solution of known concentration (the titrant). The titrant is added from a burette, drop by drop, until the reaction is complete — this point is called the equivalence point.
The Titration Equation
The fundamental relationship is: n₁ × C₁ × V₁ = n₂ × C₂ × V₂
where:
- n = number of equivalents (protons donated or accepted per molecule; 1 for monoprotic, 2 for diprotic)
- C = concentration in mol/L (molarity)
- V = volume in liters
- Subscript 1 = titrant (known); subscript 2 = analyte (unknown)
Equivalence Point vs Endpoint
The equivalence point is when stoichiometrically equivalent amounts of acid and base have reacted — moles of H⁺ equals moles of OH⁻. The endpoint is when the indicator changes color. With a perfect indicator, these coincide. In practice, a small endpoint error of 1–2 drops is acceptable.
Common Indicators and pH Ranges
| Indicator | Color change (acid→base) | pH range |
|---|---|---|
| Methyl orange | Red → Yellow | 3.1 – 4.4 |
| Bromothymol blue | Yellow → Blue | 6.0 – 7.6 |
| Phenolphthalein | Colorless → Pink | 8.2 – 10.0 |
| Litmus | Red → Blue | 5.0 – 8.0 |
Rule of thumb: Use phenolphthalein for strong acid–strong base or weak acid–strong base titrations. Use methyl orange for strong base–weak acid titrations.
Types of Acids and Bases
Monoprotic acids (1 proton per molecule): HCl, HNO₃, HF, acetic acid (CH₃COOH) Diprotic acids (2 protons per molecule): H₂SO₄, H₂CO₃, H₂C₂O₄ (oxalic acid) Triprotic acids (3 protons per molecule): H₃PO₄
Monoprotic bases: NaOH, KOH Diprotic bases: Ca(OH)₂, Ba(OH)₂
Worked Example
Problem: 25.0 mL of HCl is titrated with 0.100 mol/L NaOH. At equivalence, 32.4 mL of NaOH is used. Find [HCl].
Both monoprotic (n = 1): C_HCl × 25.0 = 0.100 × 32.4
C_HCl = (0.100 × 32.4) / 25.0 = 0.1296 mol/L
Primary Standards
A primary standard is a highly pure, stable substance used to prepare the standard solution. Common primary standards include potassium hydrogen phthalate (KHP, MM = 204.22 g/mol) for standardizing NaOH, and sodium carbonate (Na₂CO₃) for standardizing HCl. Using a primary standard ensures the titrant concentration is accurately known.