The Molarity simulation from PhET lets you change the amount of solute and the volume of a solution and watch the concentration change. You can see how the colour of the solution tells you how concentrated it is, compare different solutes, and discover when a solution becomes saturated. It is free, runs in any browser on a phone, tablet or laptop, and it is a great fit for solutions and concentration lessons in Tamil Nadu State Board (Samacheer Kalvi) Chemistry.
What is the Molarity simulation?
This interactive simulation asks a simple question: what decides the concentration of a solution? You adjust the amount of solute in moles and the volume of the solution in litres, and the concentration updates straight away. You can also switch the solute to compare different compounds in water. Because it runs on HTML5, there is nothing to install, and it works on phones, tablets, Chromebooks and computers.
High school to university
Amount of solute, volume and solute type
Phone, tablet, Chromebook, PC
English
PhET’s learning goals include describing how volume and amount of solute relate to concentration, explaining how solution colour and concentration are related, calculating concentration in mol/L, using molarity to work out a dilution, and comparing the solubility limits of different solutes.
Launch the Molarity simulation online
Tap or click inside the player and change the amount of solute and the volume. Use the full-screen button in the player for a bigger view.
Credit: University of Colorado Boulder
How to use the Molarity simulation, step by step
- Predict first. Before you change anything, say what you think will happen to the concentration.
- Add more solute. Raise the amount of solute and keep the volume fixed. Watch the concentration and the colour get stronger.
- Change the volume. Keep the solute fixed and add more water. Notice that the concentration drops and the colour gets lighter.
- Try different solutes. Switch the solute and compare how the colours and the limits differ.
- Find the saturation point. Keep adding solute and see what happens when the solution cannot hold any more.
Tip for students: change only one thing at a time. That is how you learn which variable causes which effect.
The idea behind the simulation: M = n ÷ V
M = n ÷ V
Here M is the molarity in mol/L, n is the amount of solute in moles and V is the volume of the solution in litres. More solute in the same volume gives a higher concentration. The same solute in more volume gives a lower concentration. For dilutions, the amount of solute stays the same, so M1V1 = M2V2.
Worked example: A solution has 0.5 mol of solute in 2 L. Its molarity is 0.5 ÷ 2 = 0.25 mol/L. For a dilution, if 100 mL of a 2 M solution is diluted to 500 mL, the new molarity is (2 × 100) ÷ 500 = 0.4 M. Build similar solutions in the simulation and check the colours.
Solution key terms explained
These are the words you will meet while using the Molarity simulation, with simple meanings.
Solute
The substance that dissolves, such as a salt or a dye.
Solvent
The substance that does the dissolving. In this simulation it is water.
Solution
The uniform mixture formed when a solute dissolves in a solvent.
Mole (mol)
A unit for the amount of a substance. One mole contains about 6.022 × 1023 particles.
Concentration
How much solute is present in a given volume of solution.
Molarity (M)
Concentration in moles of solute per litre of solution (mol/L).
Dilution
Adding solvent to lower the concentration. The amount of solute does not change.
Saturated solution
A solution that cannot dissolve any more solute at that temperature.
Solubility
The most solute that can dissolve in a solvent. It differs from one solute to another.
Common mistakes: Using the volume of the solvent instead of the final volume of the solution, forgetting to convert millilitres to litres, and thinking a darker colour means more solution rather than more concentrated solution.
Try the molarity calculator (practice what you explore)
Enter the amount of solute in moles and the volume of the solution in litres to see the molarity. Then tap a “what if” button.
What happens to concentration when you change a variable
| Change | Effect on concentration |
|---|---|
| Solute doubled (same volume) | Concentration doubles |
| Solute halved (same volume) | Concentration halves |
| Volume doubled (same solute) | Concentration halves |
| Volume halved (same solute) | Concentration doubles |
| Solute and volume both doubled | Concentration stays the same |
Classroom activities for teachers
The Molarity simulation fits a single 40-minute period.
- Predict and test (10 min): students write a prediction before each change, then check it in the simulation.
- Match the colour (10 min): pairs make two solutions with different amounts and volumes but the same concentration.
- Dilution challenge (10 min): students dilute a solution to a target concentration and check it with M₁V₁ = M₂V₂.
- Exit ticket (10 min): students explain in two sentences why adding water lowers the molarity.
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 solutions lessons visual. More free science simulations and textbook PDFs are on the home page.
Quick quiz: test your understanding of molarity
Score: 0 / 5
Molarity simulation: frequently asked questions
Is the Molarity 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.
What is molarity?
Molarity is the concentration of a solution, measured as the moles of solute per litre of solution. Its unit is mol/L, also written M.
What happens to molarity when you add water?
The amount of solute stays the same, but the volume goes up, so the molarity goes down. This is a dilution, and it follows M1 × V1 = M2 × V2.
The Molarity simulation turns concentration into something you can adjust, measure and see. Explore it, take the quiz above, and keep experimenting until predicting the concentration feels easy.