Date: Mon, 25 Jan 2010 11:50:38 -0500
Reply-To: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
Sender: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
From: List Moderator <ecgrants**At_Symbol_Here**UVM.EDU>
Subject: Re: Possible cause for this HS chem accident

From: "Koster Sandra K" <koster.sand**At_Symbol_Here**>

Date: January 25, 2010 11:44:50 AM EST
Subject: RE: [DCHAS-L] Possible cause for this HS chem accident

There are many examples of YouTube videos of the reaction of potassium chlorate with various candies.  See this one using a candy cane.  Sugar counts as organic matter and this is the result. ?v=bbO-1C_BP_k   YouTube will give you links to other similar videos.  These are pretty violent reactions.  The organic starts the decomposition of potassium chlorate to generate oxygen gas; hence the combustion and inability to blow out the flame.  The reaction is generating its own oxygen and it is exothermic.  If you just have to wow your high school students with this reaction make absolutely sure you follow suggestions 3 & especially 4.  The shield is crucial.  The metal base needs to be heavy and the instructor should be wearing a face shield and heavy gloves.  If they elect to use the hood sash as protection as in this video, opening the sash exposes nearby students to considerable hazard.    
Flinn Scientific=92s catalog gives several warnings for those who might purchase potassium chlorate, e.g. in part: =93=85Because this substance is so frequently a source of accidents on school premises we have elected to list some of the incompatible substances which should be avoided=85..=94 and =93Molten KClO3 is a powerful oxidizer of organic materials like the rubber in the stoppers used in the generating apparatus.  Explosions can and do result=85.=94    
If you actually want to demonstrate a chemical principle there is a much safer way to carry out a decomposition reaction to generate oxygen and relate it to the reaction stoichiometry or as a gas law experiment.  Add Baker=92s yeast to 3% hydrogen peroxide solution at room temperature.  The hydrogen peroxide is the composition available in discount stores.  You can weigh before and after to get the amount of oxygen produced and calculate the actual % hydrogen peroxide.  You can also displace water with the oxygen generated and check gas laws.  This is the method we use at University of Wisconsin-La Crosse.  There are articles in the Journal of Chemical Education about the hazards of the potassium chlorate method (1982) and detailing the proposed alternative method to generate oxygen (1988).  We use a simpler apparatus than the one in the article.  Note the dates.  This is not a new problem.  Doing a hazardous reaction many times without an accident does not prevent one from happening.
Sandra Koster
Senior Lecturer
UW-La Crosse


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