Applicable Stoichiometry: Combustion reaction of acetylene

This activity is designed to give practical application to the use of stoichiometry, chemical reaction types, lab safety, lab design and engineering, and scientific theory.

Due to the safety concerns with the ignition of acetylene gas in the combustion reaction, this lab should only be utilized with advanced chemistry students that have consistently practice safe laboratory procedures. The lab is generally conducted in a gymnasium due to the need for a high ceiling so coffee cans achieve maximum height. The activity generally takes two weeks; with the first week designated for design and stoichiometric calculations and the second for field trials. Students usually bring in their own cans and the instructor provides wire igniters and plastic trays to act as launch pads. An altimeter measurement device such as that used to measure altitude of rocket launches can be adapted mathematically to measure the individual height of the final student launches.

The lesson is used as a means by which to utilize a variety of chemical concepts in a practical setting. The instructor separates the class into groups that compete to achieve the highest altitude of a coffee can utilizing the synthesis reaction of calcium carbide and water and subsequent combustion reaction of acetylene gas and atmospheric oxygen. The students spend a week examining the stoichimetric calculations and limiting reactions for the pre-mentioned reactions and design a plan and list of independent, dependent, and control variables that will help them achieve the most efficient "lift-off" and altitude of their individual coffee cans. During the second week, the students journal daily as they run through their various designs trial and variables and attempt to perfect the "perfect" recipe of variables for the final contest day, at which point they will complete a lab write-up of their daily variable recordings. Students will also turn in to the instructor, one final set of variables and a proportional scale-up of their best resulting variables to be utilized by the instructor to launch a five gallon bucket for three trails per group, to see which group achieves the highest altitude and thus wins the contest (in my classroom I bought pizza for the winning team).

I instructed the students to announce "clear" whenever an ignition was about to commence and placed each group at least 15 ft apart from one another. The students came up with all sorts of variables, including adding water to the tray to achieve a better seal, squeezing the plastic can to vacuum some water to create a better seal, placing a rubber stopper for weight on the top of the can to achieve a better seal, etc. The launch platforms that I used were stream tables from the earth science room. The ignition device was a barbecue ignitor and a long wire (10 ft) clayed down to the stream table with the wire extending up a few inches into where the can would be placed for ignition. This can be a very wet activity and I assigned whichever group forgot to wear safety glasses or committed some lab infraction, etc. to mop up the water mess generated from the days activities.

I took a daily note of student participation for points as well as a deduction for unsafe lab procedures as I deemed necessary. The students turned in a typed lab write-up on their daily progress and normative results, discussion, etc.

1. Distinguish among hypothesis, theory and law as scientific terms and how they are used to answer a specific question.
2. Recognize that in order to be valid, scientific knowledge must meet certain criteria including that it: be consistent with experimental, observational and inferential evidence about nature; follow rules of logic and reporting both methods and procedures; and, be falsifiable and open to criticism.