The pH Scale Basics simulation from PhET is a simple way to test the pH of everyday liquids such as coffee, saliva and soap, and decide whether each one is acidic, basic or neutral. You can also see what happens to the pH when you add more liquid or dilute it with water. It is free, runs in any browser on a phone, tablet or laptop, and it is a great fit for the first lessons on acids and bases in Tamil Nadu State Board (Samacheer Kalvi) Science.
What is the pH Scale Basics simulation?
This interactive simulation is a gentle introduction to pH. You can test liquids from daily life, sort them into acidic, basic and neutral, and see how a liquid’s color goes with its pH. You can also try adding more liquid or diluting with water to see what changes. Because it runs on HTML5, there is nothing to install, and it works on phones, tablets, Chromebooks and computers.
Middle school and general chemistry
pH, acids, bases and dilution
Phone, tablet, Chromebook, PC
English
PhET’s learning goals are to decide whether a solution is acidic, basic or neutral, to order acids or bases by how acidic or basic they are, to relate a liquid’s color to its pH, and to predict how volume or dilution with water affects the pH of acids and bases.
Launch the pH Scale Basics simulation online
Tap or click inside the player and start exploring. Use the full-screen button in the player for a bigger view.
Credit: University of Colorado Boulder
How to use the pH Scale Basics simulation, step by step
- Predict first. Before you test a liquid, say whether you think it is acidic, basic or neutral.
- Test the liquid. Check its pH and note whether it is below 7, above 7, or equal to 7.
- Look at the color. Notice how the color of the liquid goes with its pH.
- Put them in order. Rank the liquids from the most acidic to the most basic.
- Try volume and dilution. Add more of the same liquid, then add water, and watch what happens to the pH.
Tip for students: write each liquid and its pH in a table. Sorting the table makes the order easy to see.
The idea behind the simulation: reading the pH scale
pH below 7 = acid, 7 = neutral, above 7 = base
The pH scale usually runs from 0 to 14. Pure water is neutral, with a pH of 7. The lower the pH is below 7, the stronger the acid. The higher the pH is above 7, the stronger the base. Each step of 1 on the scale means 10 times more or less of the ions that decide acidity. Diluting an acid with water moves its pH up toward 7, and diluting a base moves its pH down toward 7, but dilution never carries it past 7.
Worked example: A liquid with a pH of 3 is acidic. Mix 1 part of it with 9 parts of water, which is a 10 times dilution, and the pH rises to about 4. It is still acidic, just 10 times weaker.
pH key terms explained
These are the words you will meet while using the pH Scale Basics simulation, with simple meanings.
pH
A number that tells how acidic or basic a liquid is.
Acid
A liquid with a pH below 7, such as lemon juice.
Base
A liquid with a pH above 7, such as soapy water.
Neutral
A liquid with a pH of 7, such as pure water.
Dilution
Adding water to make a solution weaker.
Volume
The amount of liquid you have. Adding more of the same liquid does not change its pH.
Indicator color
A color that shows the pH of a liquid, such as red for strong acids and purple for strong bases.
Concentration
How much acid or base is dissolved in the liquid.
Common mistakes: Thinking that more liquid means a different pH, believing that diluting an acid turns it into a base, and forgetting that a lower pH means a stronger acid.
Try the dilution calculator (practice what you explore)
Enter the starting pH of a strong acid or base and how many times you dilute it with water. The calculator shows the new pH. Then tap a “what if” button.
What happens when you change a variable
| Change | Effect on the pH |
|---|---|
| Add more of the same liquid | The pH stays the same |
| Dilute an acid with water | The pH rises toward 7 |
| Dilute a base with water | The pH falls toward 7 |
| Dilute 10 times | The pH moves 1 step closer to 7 |
| Dilute a lot | The pH gets very close to 7 but does not cross it |
Classroom activities for teachers
The pH Scale Basics simulation fits a single 40-minute period.
- Predict and test (10 min): students sort liquids as acidic, basic or neutral, then check each one.
- Order the liquids (10 min): students rank the liquids from the most acidic to the most basic and compare lists.
- Dilution test (10 min): students add water to an acid and a base and record the change in pH.
- Exit ticket (10 min): students explain in two sentences why adding water does not turn an acid into a base.
Looking for the matching chapters? Browse the Science and Chemistry books on TN SchoolBooks and download the Samacheer Kalvi PDFs, then use this simulation to make the acids and bases lessons visual. More free science simulations and textbook PDFs are on the home page.
Quick quiz: test your understanding of pH
Score: 0 / 5
pH Scale Basics simulation: frequently asked questions
Is the pH Scale Basics simulation free?
Yes. PhET simulations are free to run online in a browser. Check PhET’s licensing page for reuse terms.
Does it work on a mobile phone?
Yes. It is built with HTML5 and works on phones, tablets and Chromebooks. Use landscape mode or the player’s full-screen button for a bigger view.
How can I tell if a liquid is acidic or basic?
Look at its pH. A pH below 7 is acidic, a pH of 7 is neutral and a pH above 7 is basic.
Does adding water change the pH?
Yes. Adding water to an acid raises its pH toward 7, and adding water to a base lowers its pH toward 7. Adding more of the same liquid, without water, does not change the pH.
The pH Scale Basics simulation turns the pH scale into something you can test, sort and see. Explore it, take the quiz above, and keep experimenting until sorting acids and bases feels easy.