Does your toothpaste contain lime?

cut out paper toothpaste tube attached to whiteboard

In addition to fluoride, some toothpastes also contain lime as a solid component. This serves to gently remove plaque from the teeth. You can find out whether a toothpaste contains lime with a simple experiment. Lime reacts with acids: if there is lime in the toothpaste, it will start to foam when mixed with vinegar. Does your toothpaste contain lime?

Before you get started

If you are experimenting at home:
1. Let your parents know and discuss the experiments with them beforehand.
2. Do not eat or drink at your workspace.
3. Wash your hands thoroughly before and after the experiment.
4. Be careful and cautious with the materials.

Graphic figure boy pouring liquid in flask

packages of sugar, salt, with citric acis bottle and rolling pin

You will need

Eggshells
Salt or sugar
Citric acid ‏(liquid)
Toothpaste with and/or without lime (CaCO₃)
3 glasses
Measuring jug
Freezer bag
Rolling pin

Let’s get started!

hands with rolling pin which is passed over freezer bag with eggshells

1. Grind the eggshells

Put some eggshells in a freezer bag and crush the eggshells with a rolling pin.

three glass jars with liquid, eggshell powder and toothpaste

2. Preparation

Fill 3 jam jars as follows:
2 tsp sugar (or salt)
2 tsp eggshells
2 tsp toothpaste (with lime)

3. Add citric aid

Now pour 100 ml of citric acid into each jam jar. Observe what happens.

close up of two glass jars, one with foaming liquid

4. Observe and compare

If there is lime in the toothpaste, the citric acid dissolves the lime and carbon dioxide is released. As a result, it starts to foam. If a toothpaste does not foam, it does not contain lime.