From e-how:
Acid and Base Explosion
Sometimes when acids and bases react they can cause a violent reaction. For example, when acidic vinegar mixes with alkaline baking soda, the two form carbon dioxide to create an explosion.
Test the theory at home by mixing 1/2 cup water with 1/4 cup vinegar in a plastic bag. Put 1.5 tablespoons [baking soda] in the center of a 5-by-5-inch paper towel and fold it up. Drop the folded square into the plastic bag and seal it up quickly. Shake the bag and get out of the way...because it's going to blow up and make a mess!
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