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Salt Hydrolysis

High schoolChemistryIdeal acetate and ammonium protonation equilibria with exact electroneutrality and water autoionization at 25 °C

Drag the left dose handle to add salt and the right water handle to dilute. Compare acidic, basic and near-neutral salt solutions.

3D

Drag the apparatus to adjust it. Drag the background to rotate. Scroll to zoom.

Measurement notebook

Change the setup, test a prediction and save the result. Up to 12 snapshots are kept.

About this experiment

Deliver a salt dose into water and compare neutral, acidic and basic salts. Measure pH while changing the delivered amount and dilution, then identify which ions react with water.

Learning goals

  • Classify salts through the acid-base character of their ions.
  • Connect hydrolysis with conjugate-acid and conjugate-base equilibria.
  • Observe pH approaching neutral in sufficiently dilute solutions.

How to use it

  1. 1Add a full sodium acetate dose and record the basic pH.
  2. 2Rinse and repeat with ammonium chloride, then sodium chloride.
  3. 3Compare ammonium acetate with the two salts of strong counterions.
  4. 4Dilute a fixed delivered dose and inspect the water-ionization limit on the concentration plot.

The model

These approximate 25 °C constants determine the two protonation families.
Only the species present for the chosen salt are included.
An analogous analytical mass balance applies to the ammonium family.

Assumptions

  • Solutions are ideal and closed to atmospheric carbon dioxide. No activity coefficients or other ion-pairing equilibria are included.
  • The delivery clock specifies the fraction of the salt dose introduced, not a physical dissolution rate constant. All introduced salt is assumed dissolved.
  • Virtual indicator colour aids comparison; the model salt solutions are otherwise colourless. Molar masses and pKa values are rounded teaching inputs.

Try this in class

  1. Q1Why does sodium chloride stay neutral in the model?
  2. Q2Why is ammonium acetate nearly neutral despite containing two weak acid-base partners?

Frequently asked questions

Is hydrolysis the breaking of every salt into a molecular acid and base?

No. The calculation finds the equilibrium fractions of conjugate protonation states while maintaining electroneutrality.

Does dilution always leave pH unchanged?

No. Hydrolysing salt concentrations change, and water autoionization becomes important at very low concentrations.