How to Make a Salt-Dough Volcano
Baking Soda Volcanos
Making an erupting volcano is a classic science experiment for young children. This project can be created for a science fair, as part of an earth science unit, or as part of a chemistry unit. The volcano's body is made from salt dough, which is inexpensive. The volcano can be baked and sealed with an acrylic sealer if it is intended for long-term use. There is no need to bake the dough if the volcano is made for a one-time demonstration. For use in a science project, consider painting the volcano - use acrylic paints, as tempera paints will begin to peel from the surface of the salt dough over time.
Other equipment required for the project include:
- A glass jar
- Baking dish (optional)
- Food coloring (optional)
- Acrylic sealer (optional)
- A deep dish for eruptions
- 6 cups flour
- 3 cups salt
- 3 cups water
- 2 tbs baking soda
- Few drops liquid dish washing detergent
- 1/2 cup vinegar
Salt Dough IngredientsClick thumbnail to view full-size
- Mix the flour, salt, and water in a large mixing bowl to form a smooth dough.
- Place the dough in a baking dish, and mold the dough into a volcano shape around a glass jar.
- If desired, bake the volcano at 225 degrees Fahrenheit until the dough is dry. This may take 4-6 hours. Baking the volcano will allow it to last longer.
- Paint the volcano and apply an acrylic sealer. Acrylic sealer is available at most craft stores and is easy to spray onto the finished volcano. Allow the paint and sealer to dry. This step is optional, but recommended if the volcano is meant to last for more than a single day.
- Place a few drops of liquid dish washing detergent into the glass jar. Add 2 tablespoons of baking soda. A few drops of red food coloring may also be added, if desired (this will make the eruption take on the color of the food coloring).
- To make the volcano erupt, pour in some vinegar (about 1/2 cup) and watch the "lava" flow!
Volcano Science Project
What Makes the Volcano Erupt?
This "eruption" is a chemical reaction between the baking soda (sodium bicarbonate) and the vinegar (acetic acid). There are two reactions that take place to create the bubbling foam that flows.
The first reaction is a double replacement reaction. The sodium carbonate reacts with the acetic acid to form carbonic acid.
First, the baking soda exists in the following state:
NaHCO3 <-> Na+ + HCO3
The acetic acid exists as:
CH3COOH <-> H+ + CH3COO-
When the baking soda and acetic acid are combined, the following reaction takes place to form carbonic acid ( H2CO3):
H+ + HCO3 <-> H2CO3
The second reaction that takes place is a decomposition reaction. The carbonic acid is unstable and quickly decomposes into water and carbon dioxide (a gas). The formation of the carbon dioxide gas (CO2) is what creates the foam pouring out of the volcano.
Soda and Mentos: An Alternative Reaction
For a more explosive volcano, make a salt dough volcano and mold it around a plastic soda bottle. Do not bake the volcano with the plastic bottle in place - simply use an uncured version of the dough. If desired, allow the salt dough to air dry - this will take several days in a dry, warm location.
Add soda to the bottle - diet soda is the best, as it won't create a sticky, sugary mess. Place the volcano on a table outside, and drop the Mentos candies into the bottle. A fountain of foam will quickly shoot into the air. This "eruption" is extremely impressive - and messy! Do not perform this experiment indoors, as the jet of foaming soda will make a huge mess.
This reaction occurs because the chalky surface of the Mentos candy is filled with tiny holes. This allows a physical reaction to occur (as opposed to a chemical reaction). The carbon dioxide in the soda fills the microscopic holes in the candy and begins to expand rapidly. This is a process called nucleation.