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Hydrogen and Oxygen Generating, Collecting, & Testing
Hydrogen is a clear, colorless gas which is said to be “combustible,” meaning that it can burn quite readily.
Oxygen is also a clear, colorless gas that is said to “support combustion,” meaning that it must be present for
combustible materials to burn. In this lab, you will be generating, collecting, and testing hydrogen and
oxygen gas. Hydrochloric acid is reacted with zinc to generate the hydrogen. (In general, any strong acid and
almost any metal reacts to produce hydrogen.) Hydrogen peroxide is added to manganese metal to generate
the oxygen. (Hydrogen peroxide decomposes by itself to produce water and oxygen at a slow, imperceptible
rate; the manganese oxide “rust” which coats the manganese metal acts as a catalyst to speed up this
reaction.) By collecting and pop-testing (igniting) different hydrogen/oxygen mixtures, you will audibly
compare them to determine the most reactive (loudest) mixture.
Because this lab is performed on the microscale level, the explosions, though potentially loud, are
completely safe. On the other hand, the two solutions used in this lab, hydrochloric acid (HCl) and hydrogen
peroxide (H2O2), can cause serious damage should they come in contact with your eyes.
Materials
250 mL beaker (1)
10 mL graduated cylinder (1)
small test tube labeled “H2 generator,” 1/6 full of
Candle
zinc (1)
Lighter from me
small test tube labeled “O2 generator,” 1/6 full of
1 M hydrochloric acid (HCl)
manganese (1)
3% hydrogen peroxide (H2O2)
1-hole rubber stoppers with 1" nozzles (nozzles
Permanent marker (1)
are cut from the tips of graduated pipets) (2)
tap water
cut-off graduated pipet or super jumbo pipet (1)
Procedure:
Caution: Put on your goggles and apron now!!
Record all observations
1. Fill the beaker 3/4 full with tap water. This will act as a test tube holder, a temperature
regulator, and a water reserve during the experiment.
2. Using the graduated cylinder and the pen, mark the cut-off jumbo pipet to show six equalvolume increments. This cut-off pipet will be referred to as the “collection bulb” (see figure
below).
3. Light a candle.
4. The test tube labeled “H2 generator” contains several pieces of zinc metal and is topped with a
1-hole stopper (with nozzle). Remove the stopper. Using the full length graduated pipet, add
enough 1 M HCl to fill the test tube to within 2 cm of the top. Replace the stopper and set the
generator in the beaker of water. Wait 5 seconds before beginning the next step.
5. Fill the collection bulb completely full of water. Place the end of the pipet over the end of the
generator and collect the hydrogen gas.
6. Once the collection bulb is filled with gas, hold it horizontally with its mouth roughly 1 cm
from the mid-section of the flame. Avoid putting the bulb directly in the flame. It will melt
and possibly burn. Should this happen, quench the tip in the beaker of water and obtain a new
bulb from the instructor. Gently squeeze a very small portion of the contents of the bulb into
the flame and observe. Repeat.
7. Repeat steps #4 through #6, generating, collecting, and testing oxygen this time. There are two important
differences to keep in mind. First, the test tube labeled “O2 generator” does not contain zinc; it contains
pieces of manganese metal (with an oxide coating, MnO2). Second, hydrogen peroxide (H2O2), not HCl,
will be added to the test tube.
8. While generating both gases side by side, collect and test all different possible ratios of hydrogen and
oxygen. Be as consistent as possible each time. If either of the two reactions should slow down too much,
simply remove the stopper, carefully decant (pour off) the remaining liquid into the sink, and replace it
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with some fresh solution from the appropriate stock bottle. Replace the stopper; wait 5 seconds and
resume collecting the gas.
9. Create a bar graph that shows, in a logical fashion, the relative loudness of each of the samples that you
tested (including the pure hydrogen and oxygen). 15 pts
10. Collect the optimum mixture one more time. Instead of pop-testing it with the flame, take it to the
“rocket launch pad” and have the instructor supply the activation energy with a Tesla coil. Can you think
of ways to make your rocket go farther? Try them! What ratio of hydrogen, oxygen, and water produces
the greatest distance when the rocket is launched?
11. Dispose of the liquid down the drain. Try to reserve the solids for the next person.
Questions (No Formal Lab Report): 3 ½ pts each
1. Write a balanced equation for the reaction taking place inside the hydrogen generator.
2. Write a balanced equation for the reaction taking place inside the oxygen generator.
3. Define and explain the roll of catalysts.
4. Which do you think will have to be replaced first: the zinc in the hydrogen generator or the manganese in
the oxygen generator? Explain.
5. There are two reasons for filling the generators up so full. What are they
?
6. Explain your observations for the pop-test of pure hydrogen.
7. Explain your observations for the pop-test of pure oxygen.
8. Did you find any mixtures that produced no reaction at all? Explain how that could happen.
9.
What proportion of hydrogen and oxygen produced the most explosive mixture? Why was that mixture
most explosive? (Think about volume to volume ration.)
10. Write a balanced equation for the reaction of hydrogen and oxygen.
11. Why don’t the hydrogen and oxygen in the collection bulb react as soon as they mix? What role does the
flame play?
12. If a small spark is needed to supply the activation energy for a small bulb of hydrogen-oxygen mixture,
how could the same small spark also act to supply the activation energy for an entire room-full of the
mixture? In other words, why does one not have to use a proportionately larger amount of energy to
spark a proportionately larger volume of hydrogen and oxygen? (Discuss Activation Energy)