The Carbide Lab Production of Acetylene 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.

CaO(s) + 3 C (s)  CaC2 (s) + CO(g) 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 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.