Preparation of Sterno from Blackboard Chalk
Purpose:
To create a gel similar to the commercial product Sterno from calcium acetate and isopropyl
alcohol. To determine whether a step in the process is a chemical or a physical change.
Background:
In this experiment you will produce a gel similar to the common product Sterno. A gel is a
colloidal system in which a liquid is dispersed in a solid. A colloidal system that resembles a
liquid is called a sol whereas one that resembles a solid is called a gel. The Sterno-like product
formed in this reaction is an example of a gel similar to the familiar Jello desert. Other
substances that are gels include jelly (pectin) and agar.
The solid used in this experiment is common blackboard chalk. The major components of chalk
are calcium carbonate (CaCO3) and calcium sulfate (CaSO4). The calcium carbonate will react
in this experiment. This compound will be mixed with vinegar in the following chemical
reaction:
CaCO3(s) + 2CH3COOH(aq)  Ca(CH3COO)2(aq) + CO2(g) + H2O(l)
chalk
vinegar
calcium
carbon
water
acetate
dioxide
The resultant solution will be filtered to remove the unreacted chalk. After the solution is passed
through filter paper the liquid that is produced is called the filtrate.
You will need to produce a saturated solution of calcium acetate. A saturated solution is one in
which the maximum amount of the solid (solute) is dissolved in a given amount of solution. In
this case the solute is calcium acetate and the solvent is water. The water is evaporated by
boiling it leaving behind only enough water to keep the calcium acetate dissolved completely.
You should now have a saturated solution.
The gel is formed by taking a small amount of this saturated solution and adding it to 91%
isopropyl alcohol. The liquid (alcohol) becomes suspended in the solid (calcium acetate). If too
much water is in the calcium acetate or the alcohol, the gel will not form. This gel is similar to
the commercial product Sterno. The flame produced by the combustion of the isopropyl alcohol
is quite hot, but the combustion is limited to the gel.
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Procedure:
1. Crush approximately 25 g of yellow chalk (2.5 sticks) into a course powder using the mortar
and pestle.
2. Place the chalk in a 400 mL beaker. Add 50 mL of white distilled vinegar to the chalk. Stir
the mixture with a stirring rod until the foam has subsided. After the reaction slows down add
another 50 mL of vinegar and stir the mixture for approximately 3 to 4 more minutes after the
foam subsides again. All of the chalk will not react, but you will produce plenty of calcium
acetate for the reaction.
3. Gravity filter the solution through filter paper into a 250 mL flask. The resulting calcium
acetate solution will be either clear or slightly cloudy, but the yellow colored remains of the
chalk should be filtered out of the solution. Helpful Hint: Wait until the solid has settled from
the liquid before beginning to filter.
4. A saturated solution of calcium acetate is required for the formation of the gel. Place the
filtered solution in a clean 400 mL beaker and place it on a hot plate. Boil the solution until you
have approximately 15 mL of the solution. Helpful Hint: You can begin to heat the solution
before it has all filtered by transferring it as it filters.
5. To make the Sterno, place 5 mL of the saturated calcium acetate solution from the beaker in
an evaporating dish. Add 30 mL of 91% isopropyl alcohol to the calcium acetate solution and
stir slowly. In about 15-20 seconds the mass in the container will solidify. Once the gel has
formed you can ignite it with a match. The gel will burn for approximately 15 minutes, until all
the alcohol has been used up leaving behind charred calcium acetate salt.
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