Butane Combustion Analysis Demo for a High School Chemistry Class

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SUMMARY

This discussion focuses on conducting a combustion analysis experiment using butane to demonstrate the empirical formula derivation from combustion products. The proposed setup involves using a butane torch or a bic lighter, with specific glassware configurations including 150 mL Erlenmeyer flasks filled with calcium chloride and sodium hydroxide for vapor collection and CO2 absorption, respectively. The goal is to quantitatively analyze the combustion of hydrocarbons, specifically aiming to derive the empirical formula from the masses of CO2 and H2O produced. The discussion highlights the importance of practical considerations in the setup and suggests alternatives like burning a candle for similar results.

PREREQUISITES
  • Understanding of combustion reactions and empirical formulas
  • Familiarity with laboratory glassware and setup
  • Knowledge of chemical absorbers such as calcium chloride and sodium hydroxide
  • Basic principles of gas collection and analysis
NEXT STEPS
  • Research "butane combustion analysis techniques" for detailed methodologies
  • Explore "fuel gas combustion calorimetry" for alternative experimental setups
  • Investigate the use of "candle combustion analysis" as a simpler demonstration
  • Learn about "empirical formula derivation from combustion products" for theoretical background
USEFUL FOR

High school chemistry teachers, laboratory instructors, and students interested in practical applications of combustion analysis and empirical formula derivation.

mishima
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Hi, I'm a high school chemistry teacher trying to develop a lab experience demonstrating combustion analysis. This is usually something we go through theoretically during discussion of percent composition and empirical formula. I'd like to actually perform one.

I was wondering if this could be done with a simple butane torch, or even a simple bic lighter?

I would setup the glassware to collect the vapors of the flame as follow:

--Open flame leading to long flute
--Flute going into 2-hole rubber bung in 150 mL erlynmeyer flask partially filled with calcium chloride (water absorber)
--Intake goes all the way to the bottom, submerged in the absorber
--Outlet runs to 2-hole rubber bung in second 150 mL erlynmeyer partially filled with sodium hydroxide (CO2 absorber)
--Again intake goes all the way to the bottom, submerged
--Outlet goes to vacuum

I've only ever seen this in textbook pictures and so am not really aware of any practical considerations here, especially the quantities of the absorbers required.
 
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mishima said:
--Open flame leading to long flute
"Flute," or flue? You've not begun or ended the combustion, so you're looking for qualitative demonstration of formation of CO2 and H2O?
 
Not sure of the correct term, but its basically an inverted glass funnel.

I am certainly not looking for a qualitative demonstration of the formation of those products, we have already studied combustion itself on the qualitative level. The point is to see how combustion analysis can lead to an empirical formula for the hydrocarbon being burned. Masses of CO2 and H2O are converted into mol C and mol H. A pseudoformula with fractional subscripts is then turned into an empirical formula with whole integer subscripts. Despite butane having a formula easily stated using organic nomenclature rules, I think there is value in demonstrating the procedure.
 
You're looking for CnH(2n + 2) in a poorly defined mixture,
mishima said:
simple butane torch
, which is properly LP, a mixture of C(1-5) saturated and unsaturated hydrocarbons. i.e., you are not going to get "whole integer subscripts." You might want to look at/google "fuel gas combustion calorimetry."
 
No reason it has to be butane, just looking for something on hand. How about just burning a candle?
 
mishima said:
a candle?
Same thing, a mixture.
 

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