Small additions.
Steady chemistry.
Meet the two partners that help keep pH steady. Add acid or base, watch them respond, and discover where their protection ends.
Explore → Explain → Try it yourselfHow much can it handle?
1. Choose your buffer
100 mL initially. Changing the recipe starts a fresh experiment.
2. Make a prediction
Will pH move a little or a lot? Which partner will react?
Each reagent is 1.00 mol dm⁻³. Added volume is included. Maximum 50 mmol of each per run.
Illustrative particles and colour, not an indicator or molecular scale.
Watch the reserves
Amounts after neutralisation, before the equilibrium adjustment.
The same additions to 100 mL pure water would give:
Both models include added volume. Pure water starts at pH 7.00.
Every addition leaves a trace
React first. Calculate second.
Your numbers. Every step.
Henderson-Hasselbalch, with neutralisation and dilution handled first.
Can you explain the change?
Understand the science behind the lab
A buffer contains a weak acid and its conjugate base, or a weak base and its conjugate acid. Its pH changes relatively little when small amounts of strong acid or base are added. It has a limited capacity.
Henderson-Hasselbalch: pH ≈ pKa + log₁₀(base partner / acid partner). Moles can replace concentrations in this ratio because both partners share the same solution volume. The commonly useful buffer range is approximately pKa ± 1; this is a guide, not a sharp boundary.
The probe uses an ideal monoprotic equilibrium calculation, including water (Kw = 1.00 × 10⁻¹⁴ at 25 °C), charge balance, and volume changes. It continues beyond buffer exhaustion. The worked approximation can differ for very dilute solutions or near exhaustion. Concentrations replace activities; this is a teaching model, not a laboratory formulation guide. Particle motion is illustrative and does not represent reaction speed.
Learn more: OpenStax: buffers · Explore titrations →