Fun with Stoichiometry: Humpty Dumpty Meets the Air Bag!

Humpty Dumpty sat on a wall,
Humpty Dumpty had a great fall;
All the King's horses, and all the King's men
Could not put Humpty Dumpty together again.

What if Humpty had an airbag? Design one for him and we’ll have an egg drop contest! Your objective will be to create an airbag that will allow Humpty Dumpty to survive the fall. In this activity you and your partner will design and test your own airbag system by combining baking soda (sodium hydrogen carbonate, also known as sodium bicarbonate, NaHCO3) and vinegar (acetic acid, CH3COOH) in re-closeable sandwich bags. Carbon dioxide (CO2), water (H2O), and sodium acetate (NaCH3COO) are the products of this reaction. Which product will be the gas that will inflate Humpty’s airbag?

Step 1:

Determine the chemical equation for the reaction described above and then balance the equation.

Step 2:
A. You will test out the reaction by adding 1 gram of NaHCO3 to 25 ml of vinegar in a re-closeable sandwich bag.
1. Wrap the sodium bicarbonate, NaHCO3, in a tissue before dropping it into the vinegar. This will allow you to control the reaction a bit.
2. Determine the best way to drop the wrapped NaHCO3 into the vinegar in the bag without losing any gas. You will need to flatten the bag to remove air and seal the bag as quickly as possible.
3. Drop the NaHCO3 into the vinegar and record your observations.
4. After the reaction becomes slow or stops, mix the ingredients to make sure the reaction is complete.
5. On separate paper, record your observations.

B. Pay special attention to the inflation of the bag and think about how you could change this to make a better airbag. Should the bag be fully inflated or partially inflated?

Step 3:
A. Based on the first investigation, calculate the amounts of vinegar and baking soda you would need to react to fully inflate the bag and leave the least amount of left over reactants. In other words, what is the most CO2 you can generate to fill the bag, but not have it pop open and not have leftover reactants? The following information will be useful:
  1. You will need to get the volume of the bag. Create your own plan to do this. Describe it in your electronic report and record your measurements and volume.
  2. Vinegar is a 1M solution of acetic acid (CH3COOH) in water. That means there is one mole of acetic acid in 1 liter of vinegar. The rest of the solution is water. If you use 25 ml, (0.025 liters) of vinegar, how many moles of acetic acid are you using?

Step 4:
Using your calculated values of NaHCO3 and vinegar, test your hypotheses (step 2) by experimentation to determine the best amounts of vinegar and baking soda to use in your airbag. Record all ideas, procedures, and calculations. You will need to turn all of this in with your lab report. Take photos to include in your electronic report.

Step 5:
Once you determine how to make the most efficient air bag (efficient means using the least mass of chemicals to create the maximum carbon dioxide gas), design and build a vehicle for Humpty Dumpty (a raw egg) so that when he falls, the airbag will protect him. Humpty will be dropped from a height of 2 meters and he is depending on your design for survival.

The only materials you can use for the vehicle are:
· small cardboard box or large margarine tub
· two ziplock plastic bags
· 1M solution of acetic acid (vinegar)
· Sodium hydrogen carbonate ( sodium bicarbonate), NaHCO3 (baking soda)
· Tape

assignment adapted from: Dumpty_cohort_1.doc