An Examination of Some Chemical and Physical Properties of Hydrogen, Oxygen,
and Carbon Dioxide Gas
Introduction
Single hydrogen atoms are highly reactive. Atoms of hydrogen react with other atoms of
hydrogen to form diatomic molecules, H2 (g). Hydrogen is the most abundant element in the
whole universe, making up the bulk of the stars and the matter found in space between stars.
However, hydrogen gas is relatively scarce on earth and only trace amounts are found in the
earth’s atmosphere. Most of the hydrogen atoms found on earth are (1) combined with oxygen
in the form of water, and (2) combined with organic compounds in living things and in fossil
fuels. Very little hydrogen is found in other compounds.
Hydrogen can be obtained from the decomposition of water and other compounds such as
methane, CH4. Hydrogen can be produced in the laboratory by the reaction of a metal with an
acid such as the reaction of zinc (Zn) with hydrochloric acid (HCl),
HCl(aq) + Zn(s)  H2(g) + ZnCl(aq).
In the past, hydrogen obtained from chemical reactions was used to fill balloons and blimps
because it is the least dense of all the gases. Because of its explosive nature, hydrogen gas has
been replaced by the slightly more dense but inflammable gas helium. Today, hydrogen is used
primarily as a fuel, in the commercial production of ammonia, and to hydrogenate unsaturated
fats. As a fuel, hydrogen combines with oxygen to produce water, releasing a large amount of
heat.
Single oxygen atoms are also reactive, although less so than hydrogen. Atoms of oxygen react
with other atoms of oxygen to form diatomic molecules, O2(g). Oxygen is the most abundant
element at the surface of the earth. The atmosphere contains 21 % oxygen. Water is the most
abundant compound on the earth’s surface and water is 89% oxygen by weight. The outer solid
part of the earth’s crust is made up of silica, SiO2, and other oxygen-containing minerals, with
oxygen contributing about 47 percent of the total. Altogether, oxygen makes up about 50 % of
the earth’s atmosphere, waters, and solid crust.
Many compounds that contain oxygen decompose releasing oxygen. Oxygen was first obtained
in 1774 when Joseph Priestly focused sunlight on mercury (II) oxide (HgO) with a magnifying
glass:
2 HgO(s)  2 Hg(l) + O2(g).
Peroxides, a category of compounds, decompose when heated or when a catalyst is added. A
catalyst is a substance that participates in a reaction and influences its speed without undergoing
permanent change itself. Hydrogen peroxide (H2O2, the solution your mother used on your cuts
and scrapes) is an example of peroxide that decomposes to produce oxygen.
2 H2O2(l)  2 H2O(l) + O2(g).
Leonardo da Vinci wrote in one of his notebooks, “Where flame cannot live no animal that
draws breath can live.” During the 1700’s several scientists were studying the similarities
between the processes of combustion (the process of burning an organic substance) and
respiration (the process of breathing and converting food to energy). In his studies on
respiration, Antoine Lavoisier put a sparrow in a bell jar filled with air, allowing the bird to die.
He observed that the air breathed by the sparrow had changed and become similar to the gas
produced when charcoal is burned. He concluded that the respirable part of air (oxygen) is
converted into carbon dioxide as it passes through the lungs. Our current understanding of
respiration and combustion are not substantially different from Lavoisier’s conclusion. Lavoisier
died by the guillotine during the French revolution. The combustion of hydrocarbons
(compounds composed of only the elements carbon and hydrogen) produce carbon dioxide and
water. The combustion of methane (CH4) is shown below.
CH4(g) + 2 O2(g)  CO2(g) +2 H2O(g).
Carbon dioxide dissolves in water to form carbonic acid. Carbon from this source may then
react with other compounds and precipitate to form carbonate rocks and minerals. The largest
reservoir of carbon on earth is in the form of carbonate rocks. The compound calcium carbonate,
present in many rocks, will react with acid to produce carbon dioxide gas.
CaCO3(s) + 2 HCl(aq)  CaCl2(aq) + H2O(l) + CO2(g).
Sodium bicarbonate, baking soda will react similarly with acid.
NaHCO3(s) + HCl(aq)  NaCl(aq) + H2O(l) + CO2(g).
Materials











6 test tubes
A test tube rack
A test tube holder
Spatulas
Zinc metal (Zn)
Plastic droppers
6 M hydrochloric acid (HCl)
Hydrogen peroxide (H2O2)
Potassium permanganate (KMnO4)
Baking soda (sodium bicarbonate, NaHCO3)
Alka-Seltzer
Procedure
1. Place approximately 2 mL (approximately 1 inch) of 6 M HCl in a clean test tube. Carefully
drop 3or 4 small pieces of zinc into the test tube with the acid. Invert an empty test tube (turn
and empty test tube upside down) over the tube in which the reaction is occurring to collect
the gas being produced. Record your observations in your laboratory notebook. Remember
to use all of your senses to make observations. Once the reaction has slowed down light a
wooden splint and quickly move the burning splint and test tube so that the flame is near the
mouth of the inverted (upside down) test tube used to collect the gas. Record your
observations in your laboratory notebook.
2. Place approximately 2 mL (approximately1 inch) of hydrogen peroxide in a clean test tube.
Carefully add about ½ inch of potassium permanganate (a catalyst) on the end of a spatula to
the test tube. Invert an empty test tube over the tube in which the reaction is occurring to
collect the gas being produced. Record your observations in your laboratory notebook. Once
the reaction has slowed down light a wooden splint and quickly move the burning splint and
test tube so that the flame is near the mouth of the inverted (upside down) test tube used to
collect the gas. Record your observations in your laboratory notebook.
3. Place approximately 2 mL (approximately1 inch) of 6 M HCl in a clean test tube. Carefully
add about 1/2 inch of baking soda (sodium bicarbonate, NaHCO3) on the end of a spatula to
the test tube. Invert an empty test tube over the tube in which the reaction is occurring to
collect the gas being produced. Record your observations in your laboratory notebook. Once
the reaction has slowed down light a wooden splint and quickly move the burning splint and
test tube so that the flame is near the mouth of the inverted (upside down) test tube used to
collect the gas. Record your observations in your laboratory notebook.
Reaction
Observations (Including color, odor1, physical
state, changes in physical state, changes in
temperature, etc.)
Identity of the
Gas Produced
1
2
3
1
Never place a chemical directly under your nose and inhale! This could be hazardous to your health.
Many compounds have sufficiently strong odors that you can detect them from a distance.
On your own
Design a test to determine what gas is produced when you add an Alka-Seltzer tablet to water.
Discuss your proposed test with your instructor and record your proposed test in your lab
notebook.
Carry out your proposed test and record your observations in your lab notebook.
Based on your results, what gas is produced when you add an Alka-Seltzer tablet to water?