Acid-Base Neutralization Calculator
Calculate the volume or concentration needed to neutralize an acid or base.
Supports HCl, H₂SO₄, H₃PO₄, NaOH, Ca(OH)₂, and custom compounds.
Acid-base neutralization occurs when the equivalents of acid exactly equal the equivalents of base.
The fundamental equation:
M_acid × V_acid × n_acid = M_base × V_base × n_base
Where:
- M = molarity (mol/L)
- V = volume (L or mL — must be consistent)
- n = number of H⁺ (for acids) or OH⁻ (for bases) per formula unit
n-factor values:
| Compound | Formula | n |
|---|---|---|
| Hydrochloric acid | HCl | 1 |
| Nitric acid | HNO₃ | 1 |
| Acetic acid | CH₃COOH | 1 |
| Sulfuric acid | H₂SO₄ | 2 |
| Phosphoric acid | H₃PO₄ | 3 |
| Sodium hydroxide | NaOH | 1 |
| Potassium hydroxide | KOH | 1 |
| Calcium hydroxide | Ca(OH)₂ | 2 |
| Aluminum hydroxide | Al(OH)₃ | 3 |
Why n matters: 1 mole of H₂SO₄ neutralizes 2 moles of NaOH (because H₂SO₄ donates 2 H⁺). 1 mole of Ca(OH)₂ neutralizes 2 moles of HCl (because Ca(OH)₂ provides 2 OH⁻).
Titration endpoint: At the equivalence point, the solution contains only salt and water (for strong acid/base). For example: HCl + NaOH → NaCl + H₂O (neutral solution). H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
Indicators: Phenolphthalein: colorless below pH 8.2, pink above. Good for strong acid/strong base. Methyl orange: red below pH 3.1, yellow above 4.4. Good for strong acid/weak base.
Why the n-factor matters more than people expect
The n-factor is the number of protons an acid can donate or a base can accept, and forgetting it is the single most common way to get this calculation wrong. Sulfuric acid donates two protons, so a 0.1 M solution delivers 0.2 moles of acid equivalents per litre. Neutralising it takes twice as much sodium hydroxide as an equally concentrated hydrochloric acid solution would.
Put another way: molarity tells you how many molecules are in the bottle, but neutralisation is a reaction between protons and hydroxides, not between molecules. Work in equivalents, which is molarity times the n-factor, and the arithmetic stops surprising you.
Reading the titration curve
The curve this calculator draws is flat at both ends and nearly vertical in the middle. That steep section is what makes titration a usable technique at all: near the equivalence point a single drop swings the pH by several units, so the colour change of the indicator is sharp rather than gradual. If your curve rises smoothly with no sudden jump, you are almost certainly titrating a weak acid against a weak base, and no indicator will give you a crisp endpoint. Use a pH meter for that case.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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