Experiment #3 / Unit 5
Hydrogen Soda Bottle Rocket
Introduction:
There are a number of metals that will react with a strong acid to produce
hydrogen gas. In these single replacement redox reactions, the metal added is
more "active" than the hydrogen in the acid and will "replace" it by way of
oxidation-reduction. The following is the general reaction:
M(s) + HA(aq)  MA(aq) + H2(g)
unbalanced
You will work with zinc and concentrated hydrochloric acid. The hydrogen
gas produced will be collected in a plastic soda bottle. We will perform a number
of measurements and calculations employing the gas laws to study the concept
of molar volume. You will also have the opportunity to "explore" the flammability
and power of H2 gas by creating a soda bottle rocket. We will see who can create
the best hydrogen propulsion vehicle!
Pre-lab:
1. Determine how much hydrogen you would like to collect to create the ideal
combination of gases for the best reaction.
2. Based on the amount of hydrogen gas you wish to collect, you will need to
back-calculate to determine how much metal will be required to produce your
desired amount of hydrogen.
Procedure:
1. Mass about 0.5 g over the determined amount of zinc just to make sure our
limiting reactant doesn’t become limiting before we want it to and the reaction
will get too slow as the zinc supply diminishes.
2. Record the barometric pressure.
3. Obtain a large test tube, stopper/tube assembly, rubber tubing, collection
trough, 3 L clear soda bottle, 400 mL beaker, and a plastic ruler.
4. Fill the collection trough about ¾ full with water. Fill the 3 L bottle with water
and invert in the trough without allowing any air to enter the bottle.
5. Pour 40 mL of 3M HCl into the test tube and prepare the tubing and stopper
for collection. When you are ready with the stopper, add the metal and quickly
stopper the test tube so as to prevent H2 gas from escaping. Sit the test tube
in the beaker.
6. Collect the H2 produced by water displacement. Collect the gas until you
reach the desired volume. Mark the water/gas level on the side of the bottle
using a piece of tape. Measure the difference in water levels between the
collection trough and the bottle with the ruler. Record the room and water
temperatures.
7. Lift the bottle and allow the remaining water to drain out. Keep the bottle
upside down (H2 is far less dense than air) and capped until you are ready to
make H2O. One chemist should hold the bottle in an extended arm while the
other chemist uses an extended arm and pair of tongs to hold a lit match at
the opening of the bottle. Note where your bottle is aimed before firing.
Chemistry II
Cary Academy
W.G. Rushin
1
8. Fill your bottle to the gas line with water than pour this into a large graduated
cylinder in order to find the volume of gas collected. Remember that the hydrogen
gas collected will be “wet” because it is contaminated with water vapor.
Data:
 mass of metal sample
 barometric pressure
 room temperature
 water temperature
 the vapor pressure of the water at this temp.
 difference in water levels (mm) - was it higher inside or outside the soda bottle?
 the volume of “wet” gas collected
Predictions:
1. Show work for the prediction of the volume of hydrogen needed.
2. Show work for the prediction of how much zinc was required.
Calculations and Questions:
1. Write the balanced total molecular equation for all three reactions. Consider
the match to be burning cellulose (C6H10O5).
2. Write a balanced net ionic equation for the production of hydrogen. Show
electron gain and loss. Identify which atom was oxidized/reduced and which
compound served as the oxidizing/reducing agent.
3. How much potential energy is represented by the bond in diatomic hydrogen?
4. Calculate the enthalpy change for the synthesis of water. How much heat should
have been produced from the reaction of your hydrogen?
5. Calculate the entropy change for the synthesis of water. Did the system increase
or decrease in disorder?
6. Calculate the free energy change for the synthesis of water. How much free
energy is gained or lost during the synthesis of your water molecules?
7. Calculate the partial pressure of hydrogen (pH2).
8. Convert the volume of “dry” hydrogen gas to STP.
9. Using the balanced equation and the amount of metal you started with,
predict how many moles of hydrogen gas should have been produced. Not a
great prediction since we didn’t use all of the metal.
10. Calculate your experimental molar volume using results from #8 and 9.
11. Calculate your percent error based on your experimental molar volume using
22.433 L/mol as the accepted molar volume for H2.
Lab Report #5.3:
 title page
 abstract
 procedure sheet
 data
 predictions
 calculations and questions
Chemistry II
Cary Academy
W.G. Rushin
2