Mrs. B’s Chemistry ~ Granada Hills High School
Spring 2003
The Carbide Lab
Production of Acetylene
Introduction
and Chemical Reaction
Discussion
Preparation of CaC2
• Limestone is a carbonate rock known chemically
as calcium carbonate. It is commonly found in the
earth’s crust. When limestone is subjected to
high heat, it decomposes into calcium oxide,
(CaO). This compound is commonly called
“lime.”
• Coke is another decomposition product of a
commonly found substance in the earth’s crust,
coal. It is simply a form of carbon.
• Both limestone and coal are inexpensive and in
abundant supply.
Preparation of CaC2
• Calcium carbide can be prepared by
heating calcium oxide (lime) with coke.
• This heating process, called “roasting,”
produces the calcium carbide (CaC2). It
is done in large ovens by way of the
following chemical reaction:
CaO(s) + 3 C (s)  CaC2 (s) + CO(g)
Formation of Acetylene Gas
• Calcium carbide, CaC2, reacts with
water to form acetylene gas, C2H2.
• Write and balance the chemical reaction
and see if you can determine what other
product may be produced.
• Include the predicted states of all
reactants and products.
Formation of Acetylene Gas
CaC2 (s) + H2O(l)  C2H2 (g) + Ca(OH)2(s)
• If you predicted that calcium oxide was a
product of this reaction, you are still correct
because it is possible that this may be one of
the products.
• Calcium oxide, CaO, when placed in water
does react to form Ca(OH)2 so if any CaO is
formed it is quickly converted to calcium
hydroxide due to the excess water usually
present in this reaction.
Combustion of Acetylene
• What will the complete combustion of
Acetylene gas produce?
• Write the balanced equation for this
standard combustion reaction.
Combustion of Acetylene
• Carbon dioxide and water vapor are the
standard products of any combustion
reaction. (… Yes, we learned this earlier last year!)
C2H2 (g) + O2 (g)
 CO2 (g) + H2O(l)
• But what if the combustion is not complete?
• What other side products may be possible?
Incomplete Combustion
of Acetylene
• Ash? Soot? What elements or compounds
are found in ash or soot?
– carbon and carbon products
• What other gases might be produced?
– carbon monoxide (CO(g))
– water vapor H2O(g)
Laboratory Activity
• The purpose of this activity is to
experimentally determine the exact
stoichiometric ratio of acetylene to oxygen to
produce the most complete combustion
reaction.
• So how can you tell it is complete?
• Other side products such as ash and soot will
not be evident upon combustion.
Laboratory Activity
• By experimentally adjusting the amount
of acetylene to air ratio in your
combustion tube and recording your
results, you can determine the best
possible ration of atmospheric air to
acetylene that gave the loudest “pop”
with the least amount of ash.
Laboratory Activity
• Devise a Data Table to contain your
collected data for this activity. Be sure
to include a large column for your
detailed observation of each
combustion reaction.
Laboratory Activity
• By measuring the total volume of the combustion
tube with a graduated cylinder you can determine the
exact ratio of air to acetylene.
• Varying the volume (mL) of water in your combustion
tube prior to collecting the acetylene gas will
determine exactly how much acetylene (mL) was
used in each reaction as this is the volume that will
be displaced by the gas generated in the reaction.
• Final calculations can determine what proportion of
oxygen was contained in the air sample of each
reaction.
The Sea-level Composition of Air
(in percent by volume at 25 ° C 101325 Pa)
is given below:
Name
Symbol
Percent by Volume
Nitrogen
N2
78.084 %
Oxygen
O2
20.9476 %
Argon
Ar
0.934 %
Carbon Dioxide
CO2
0.314 %
Neon
Ne
0.001818 %
Methane
CH4
0.0002 %
Helium
He
0.000524 %
Krypton
Kr
0.000114 %
Hydrogen
H2
0.00005 %
Xenon
Xe
0.0000087 %
Laboratory Data Table
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Be sure your Data Table contains cells for a minimum
of 6-7 trials with information noting the following:
Total Volume of Combustion Tube
Volume of acetylene used for each trial
Volume of air used for each trial
Observation of each trial:
– color of flame
– rate of reaction
– presence or quantity of ash/soot
– loudness of combustion “pop,”
– other observations made with each trial.
One Additional Column for Air to Oxygen %
calculation.