Chemistry · Acids and bases

Acid-Base Titration and pH Explorer

A burette adds sodium hydroxide, NaOH, to 25.00 mL of an acid in a flask. Move the slider to add titrant, watch the flask change color, and read the pH at every point on the titration curve.

Switch between a strong acid, a weak acid, and a weak acid with a very small Ka. Then choose an indicator and see whether its color change lands on the steep part of the curve. Record points to build your own table.

Model notes

The pH at each volume comes from solving the charge balance exactly with Kw = 1.0 × 10⁻¹⁴ at 25 °C. It does not use the usual shortcuts, so it stays correct near the equivalence point where shortcuts fail.
Acid strengths: acetic acid Ka = 1.8 × 10⁻⁵ (pKa 4.74). The ammonium ion has Ka = 5.6 × 10⁻¹⁰ (pKa 9.25), found from Kb of ammonia, 1.8 × 10⁻⁵. Activities are treated as equal to concentrations, so very precise lab pH meters will read slightly differently.
The composition bars use stoichiometry only: moles of acid left, conjugate base formed, and hydroxide in excess. They are a bookkeeping view and ignore the small equilibrium adjustments.
Indicator transition ranges are textbook values: methyl red 4.4 to 6.2, bromothymol blue 6.0 to 7.6, phenolphthalein 8.2 to 10.0. The endpoint here is where the indicator is halfway through its color change.

Sources

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