Butane Combustion Analysis Demo for a High School Chemistry Class

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Discussion Overview

The discussion centers around the feasibility of conducting a combustion analysis lab for high school chemistry students, specifically using butane or other readily available fuels. The aim is to demonstrate how combustion analysis can lead to determining the empirical formula of hydrocarbons through the collection and analysis of combustion products.

Discussion Character

  • Experimental/applied
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • A high school chemistry teacher proposes using a butane torch or lighter for a combustion analysis lab, detailing a setup involving calcium chloride and sodium hydroxide to absorb combustion products.
  • One participant questions the terminology used, suggesting clarification on whether the setup is intended for qualitative or quantitative analysis of combustion products.
  • The teacher clarifies that the goal is to quantitatively analyze the combustion products to derive an empirical formula from the masses of CO2 and H2O produced.
  • Another participant points out that using butane may not yield whole integer subscripts due to the nature of the combustion products, suggesting that the mixture may contain various hydrocarbons.
  • A suggestion is made to consider burning a candle as an alternative fuel source for the experiment.
  • Another participant responds that burning a candle would also involve a mixture of hydrocarbons, similar to butane.

Areas of Agreement / Disagreement

Participants express differing views on the suitability of butane and candles for combustion analysis, with some suggesting that both may not provide the desired clarity in empirical formula determination due to the complexity of the mixtures involved. The discussion remains unresolved regarding the best approach for the lab demonstration.

Contextual Notes

Participants have not reached a consensus on the specific fuel source or the methodology for the combustion analysis, highlighting potential limitations in achieving clear empirical formulas from the combustion of complex mixtures.

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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