Buffer Solution Simulator
Add acid and base to a buffer and to plain water side by side and watch which one resists pH change.
Add drops of acid or base to both beakers and compare. The buffer barely moves; the water swings wildly.
About the Buffer Solution Simulator
Free buffer simulator. Choose a weak acid and its salt, add strong acid or base drop by drop, and compare the pH of the buffer with plain water using the Henderson-Hasselbalch equation. Built for chemistry, the buffer solution simulator runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Add acid and base to a buffer and to plain water side by side and watch which one resists pH change. Use it to explore chemistry ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Buffer Solution Simulator
- Use the controls to change Weak acid strength (pKa), Weak acid HA, Conjugate base A⁻. The simulation reacts instantly.
- Pick an option such as Acetic acid (4.76), Carbonic acid (6.35), Ammonium (9.25) to switch modes or load an example.
- Press "+ HCl 1 mL", "+ NaOH 1 mL", "+ HCl 5 mL", "+ NaOH 5 mL" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Add 10 drops of HCl to the buffer and to water and compare.
- Increase both concentrations to raise the buffer capacity.
- Set [A⁻] = [HA] and read the pH: it equals the pKa.
- Keep adding base until the buffer breaks.
Key ideas you can learn
- A buffer contains a weak acid (HA) and its conjugate base (A⁻) that neutralise added acid or base.
- Henderson-Hasselbalch: pH = pKa + log([A⁻] / [HA]).
- A buffer works best when [A⁻] ≈ [HA] and has a limited capacity.
Where this is used in the real world
Blood, seawater, shampoo, medicines and food all use buffers to keep pH steady. Your blood pH must stay near 7.4 and is kept there mostly by the bicarbonate buffer.
Who is this simulation for?
Chemistry students from middle school to university, teachers who need a virtual demonstration, and anyone without access to a lab. It is safe, free and repeatable as many times as you like.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
How does a buffer resist pH change?
Added acid reacts with the conjugate base A⁻, and added base reacts with the weak acid HA. Both reactions use up the added ion instead of letting the pH swing.
When does a buffer stop working?
When one of the two components has been used up. Then extra acid or base changes the pH just as in plain water.
Is the Buffer Solution Simulator free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Buffer Solution Simulator work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.