Acids and Bases

About this simulation

This simulation links the pH scale to the particles in a solution. Students slide the pH between 0 and 14 and see the balance of hydrogen ions and hydroxide ions change, with grey spectator ions keeping the charge balanced. Agitation changes how fast the particles move and a toggle hides the spectators. Readouts give the pH, the true concentration of H+ and OH- and whether the solution is acidic, neutral or basic. It is useful for teaching that each pH step is a tenfold change and that the two ion concentrations multiply to a constant.

What students can explore

Move pH from 7 to 3 and read how [H+] changes in the readout.
Slide pH to 11 and compare [OH-] with [H+] and the Solution label.
Set pH to exactly 7 and check that [H+] and [OH-] are equal.
Turn off Spectator ions to see only the ions that set the pH.
Change Agitation to speed up or slow down the particles without changing the pH.

Learning objectives

1Define pH as a measure of hydrogen ion concentration.
2Explain that each pH unit is a tenfold change in [H+].
3Classify solutions as acidic, neutral or basic from their pH.
4Describe the relationship between [H+] and [OH-] in water.

Questions teachers ask

Is it free?

Yes. It is free to use in any modern browser, including tablets and interactive whiteboards, and requires no sign-up.

What does pH mean?

pH is the negative base-10 logarithm of the hydrogen ion concentration. A pH of 3 means [H+] is 0.001 mol per litre, which is ten times more than at pH 4.

Why are [H+] and [OH-] linked?

In water at 25 degrees Celsius the product [H+] times [OH-] is always 1.0 times 10 to the minus 14. When one goes up the other must go down, and at pH 7 they are equal.

How do I use it in class?

Drag the pH slider and watch the particles and readouts update. Use Agitation to change particle speed and the Spectator ions toggle to show or hide the other ions.

Embed this simulation

Drop it into your LMS, blog, or class site — free.

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Continue exploring

Compare strong and weak acids and bases at equal concentration. Dilute them and inspect hydrogen and hydroxide ions.

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Add sodium hydroxide to hydrochloric or acetic acid. Compare the titration curve, indicator colour and equivalence volume.

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Run a virtual titration. Drag the burette tap to drip sodium hydroxide into an acid, click for single drops, pick the acid and indicator, and watch the flask colour and pH change sharply at the equivalence point.

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A ribosome reads an mRNA strand that students build one base at a time. Each three-base codon brings a tRNA and adds an amino acid until a stop codon ends the protein.

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Explore an adult male reference body in 3D. Reveal 14 anatomical systems, search thousands of named structures, isolate organs, and pull 2,209 modeled pieces apart to see how the body is organized.

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From model to evidence

Use a worksheet to capture predictions, observations, and explanations after students explore.