Lava is molten rock (a liquid) that flows on the earth’s
surface. Lava is formed inside the crust of the Earth by extreme heat; it
erupts to form a volcano. During an eruption, many changes occur to the
lava. First, as it cools, the lava changes state, from liquid to solid.
Another change is the escape of gasses such as carbon dioxide, hydrogen
sulfide, and water vapor, from the lava into the atmosphere.
In this lab, the students will model a volcanic
eruption in order to simulate the chemical changes that occur in an erupting
volcano. The children will see a solid (baking soda) and liquid (vinegar)
mixing to form a gas (carbon dioxide) and a liquid.
STATES OF MATTER IN AN ERUPTING
carbon dioxide, hydrogen
- Before lab, assemble the vinegar, baking soda, clay, and red food
coloring. If you do not have clay available, you can conduct the
experiment in a plastic cup, flask, or test tube. If you are unfamiliar
with the vinegar-baking soda reaction, you may wish to try it a few
times, until you get a feel for the quantities of reactants necessary.
Shape the clay into a "volcano" as a model for your students.
Make sure you leave room at the top to place about a spoonful of baking
- The students should be familiar with images of erupting volcanoes. You
may want to show students pictures from the unit on Volcanoes from the
Plate Tectonic Cycle.
- Explain to the students that during the eruption of a volcano, all the
states of matter are present. Rocks are solids. Liquid is represented by
the lava. Many gasses are emitted by the lava during an eruption. Plasma
may even be present, in the form of electrical discharges in the sky
above the erupting volcano.
- Tell the students that today they will make a play volcano and observe
three states of matter: solid, liquid, and gas.
- Instruct the students to build a small volcano with clay, leaving a
small crater-like opening on the top. The students will be able to clean
the clay volcano, so the clay can be reused.
- Students should first place about 2-5 ml teaspoons of baking soda in
the crater at the top of the volcano. Next, mix 100 ml of vinegar with a
few drops of red food coloring (to make it look like a real volcano).
Ask the students to pour the vinegar slowly on the baking soda. The
resulting mixture will fizz as the vinegar reacts with the baking soda.
Make sure they realize that the fizz is the release of a gas (carbon
- Discuss with the students that what they have demonstrated is a
chemical change. When vinegar (a liquid) is poured on baking soda (a
solid), it produces a change to carbon dioxide (a gas).
- Explain that the gas escapes into the atmosphere, but some liquid and
solid remain in the "volcano".