Reaction in a Plastic Baggie
Science Concept: A chemical reaction between two solids creates a gas to fill up a plastic bag.
Materials & Pre-Demo Preparation: Small plastic Ziplock bag
7 g of baking soda
11 g of calcium chloride
10 ml phenol red solution
Small vial for phenol red solution
Phenol red solution is made by adding four drops of phenol red to 10 ml of distilled water. Measure out the baking soda and calcium chloride prior to the demo and put each in a separate beaker. Put the phenol red solution in a small vial that will fit inside the bag.
Directions: In the Ziplock bag, put the baking soda in one corner and the calcium chloride in the other corner. Set the bag on the table and place the vial of phenol red solution upright between the two powders. Take the cap off, pour the solution over both corners of the bag, and quickly seal the bag. Shake and tip the phenol red solution over the calcium chloride and baking soda and feel for temperature changes and notice as the bag fills with gas.
Introduction & Commentary: How many of you like balloons? Do you like blowing them up? Sometimes that can make you kind of tired, though. I'm going to show you a way in which this plastic bag will fill up like a balloon, without having to blow air into it.
Explanation: A chemical reaction occurs between the calcium chloride and the baking soda in which a double replacement reaction takes place. The two solids switch partners and form a new substance--the precipitate calcium carbonate. As the precipitate is formed, the bicarbonate breaks down first to make hydrogen ions, an acid. This acid then converts some of the bicarbonate to carbon dioxide gas which begins to blow up the plastic bag.
Also, as part of the chemical reaction between these two solids, a change in temperature can be felt--in one corner of the bag, an exothermic reaction causes the calcium chloride gets warm, while in the other corner an endothermic reaction makes the baking soda gets cold.
Calcium chloride + baking soda (sodium bicarbonate) --- calcium carbonate + sodium chloride + hydrogen ions
CaCl2 + 2 NaHCO3 ---> CaCO3 + 2 NaCl + H+ ions
Hydrogen ions + sodium bicarbonate ---> carbon dioxide + water + sodium ions
H+ ions + NaHCO3 ---> CO2 + H2O + Na+
Safety Precautions: When handling the phenol red, use caution. If it contacts skin or clothing, it may stain. Additionally, be careful in letting the bag fill up with gas. If it gets too full, the bag might pop.
Waste Disposal: Dispose of the plastic bag and its contents in the trash.