Name: ______________________________________________________Date: _______________
Finding the Ratio of Oxygen to Hydrogen in a Reaction
Purpose
The purpose of this experiment is to generate hydrogen and oxygen gas and then determine the
optimum ratio for the resulting combustion reaction. The optimum ratio will be used to calculate the
experimental mole ratio for the reaction of hydrogen and oxygen and compare it to the theoretical
ratio.
Pre-Lab Questions
1. Write the balanced chemical equation for the single replacement reaction of zinc metal and
hydrochloric acid to generate hydrogen gas and aqueous zinc chloride.
2. Write the balanced chemical equation for the manganese dioxide-catalyzed decomposition of
hydrogen peroxide to generate oxygen gas and water. Note: Since a catalyst is not really a
reactant or product, it is usually written over the arrow.
Safety Precautions!
Hydrochloric acid is toxic by ingestion and inhalation and is corrosive to skin and eyes. Hydrogen
peroxide is a skin and eye irritant. Avoid contact of all chemicals with skin and eyes and notify your
teacher immediately in the case of a spill. Wear chemical splash goggles and chemical-resistant
gloves and apron. Wash hand thoroughly with soap and water before leaving the laboratory. Do
NOT generate more hydrogen than what is in the pipette. If caught doing this, you will be sent
directly to the office.
Procedure
Part 1: Construct gas generators
1. To make gas-collecting bulbs (rockets), trim off the tip of four disposable pipets, leaving a 0.5 cm tip, as shown
in Figure 1.
2. Set up two test tubes in a test tube rack, and place a gas delivery rubber stopper into each test tube as shown in
Figure 2.
Name: ______________________________________________________Date: _______________
Figure 1: Disposable pipet
bulb with trimmed tip
(not drawn to scale)
Figure 2: Gas delivery test
tubes (not drawn to scale)
Part II: Calibrate Gas Collection Bulbs (Rocket)
1.
2.
3.
4.
Fill a beaker with water
Immerse one of the rockets under the water, and completely fill with water.
Squeeze the water into a graduated cylinder, and record the total volume of the rocket.
Determine how to divide the bulb into six equal volumes, then use the graduated cylinder to add volumes of
water needed to calibrate the pipet bulb into sixths. Mark the volume levels on the pipet bulb with a permanent
marker.
Part III: Collect and Test Hydrogen and Oxygen Gases
1. Label one of the collecting test tubes “hydrogen gas dispenser” and the other “oxygen gas disperser.”
2. Place four pieces of mossy zinc into the bottom of the “hydrogen gas dispenser” test tube. Add 3M hydrochloric
acid, and cap the test tube with the gas delivery stopper.
3. Totally fill one of the calibrated pipet bulbs with water, and place the bulb over the “hydrogen gas dispenser” test
tube to collect hydrogen gas by water displacement. As the gas enters the calibrated pipet bulb, the water will
flow out of the bulb and down the sides of the test tube. Place some paper towels under the test tube to collect
the water.
4. As soon as the rocket is filled with hydrogen, remove it and place a finger over the mouth of the rocket to
prevent the gas from leaking out.
5. Hold the rocket so the opening is up and use a burning splint to determine the relative loudness of the pop.
Record results.
6. To the test tube labeled “oxygen gas disperser,” add MnO2 powder—just a pinch. Then, add 3 % hydrogen
peroxide. Cap the test tube with a gas delivery stopper.
7. Repeat steps 2-5 with the oxygen gas generator.
Part IV: Collect and Test Oxygen/Hydrogen Gas Mixtures
1. Totally fill a calibrated pipet bulb with water, and collect oxygen gas to 1/6 full, quickly remove it and place it on
the hydrogen generator, and collect hydrogen gas in the remaining 5/6 until full. Remove from generator and
determine loudness by “pop test.” Record relative loudness of the pop.
2. Test other ratios (2:4, 3:3, 4:2, 5:1) of oxygen to hydrogen. Always collect oxygen first. Record results of
relative loudness.
Name: ______________________________________________________Date: _______________
3. Determine the ratio that produces the loudest mixture.
4. In your discussion, compare the experimental ratio that produced the loudest pop to the theoretical
stoichiometric ratio (as seen in the balanced equation for the reaction of hydrogen and oxygen gases)
for the reaction between oxygen and hydrogen gas.
Data Table
“pop-test” Properties hydrogen gas
“Pop – test” Properties of oxygen gas
Oxygen:Hydrogen Mole Ratio
1:5
2:4
3:3
4:2
5:1
Relative Loudness
Post Lab Questions
1. Draw a bar graph to illustrate the relative loudness produced by pop-testing various
oxygen/hydrogen gas mixtures.
2. Explain the relative loudness of pure oxygen and pure hydrogen in the pop-test
3. Write a balanced chemical equation for the combustion reaction of hydrogen and oxygen to
give water.
4. Complete the following sentence to describe the number of moles of each reactant involved
in the combustion of hydrogen: ______moles of hydrogen react with _____ mole of oxygen
to give _________ moles of water.
2H2 (g) + O2 (g)  2H2O(l)
When the reactants in a mixture are present in the exact mole ratio given by the balanced chemical
equation, all of the reactants should be used up when the reaction is over. There will be no
“leftover” reactants.
However, if one of the reactants is present in an amount greater than its mole ratio, then that
reactant cannot react completely, and some of it will be left over at the end of the reaction.
Use the mole ratio of hydrogen to oxygen from Question #4 to determine what happens when
various hydrogen/oxygen gas mixtures are allowed to burn. Complete the following table to indicate
which reactant is present in excess, and how much of it will be left over after the combustion
reaction is complete.
Note: The second one has been completed as an example.
Name: ______________________________________________________Date: _______________
Parts H2 6
Parts
0
O2
Which
reactant
is
present
in
excess?
How
uch of
that
reactant
is left
over?
5
1
4
2
3
3
2
4
1
5
0
6
H2
3
6.Which oxygen/hydrogen gas mixture produced the most explosive mixture? Explain why this
mixture was most explosive.
7. Why do the hydrogen and oxygen gas mixtures in the collection bulb not react as soon as they
are collect? Note: Consider the role of the match and the properties of gas molecules at room
temperature.
8. Determine the molar mass each of hydrogen, H2 and O2 gases.
9. Now determine the relative molar mass of “air” which is 80% N2 and 20% O2.
(0.80) ( molar mass of N2) +
(0.20)(molar mass of oxygen) = ?
10. Based upon your calculations from Questions 8 and 9-a) is hydrogen (more, less) massive than air?
b) is oxygen (more, less) massive than air?
11. Think about your instructions and your determination in #10—why were you told to generate
oxygen FIRST and hydrogen last?