From: "Clark, Eric J" <CLARKEJ**At_Symbol_Here**LATTC.EDU>
Subject: Re: [DCHAS-L] Iodine clock reaction waste
Date: Fri, 11 Oct 2019 13:48:33 +0000
Reply-To: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**PRINCETON.EDU>
Message-ID: BYAPR03MB45971C1E4334CEEC31564DEFB6970**At_Symbol_Here**

Hello Pamela,

For the Briggs-Rausher Reaction (aka the Iodine Clock Reaction), according to Shakhashiri, Chemical Demonstrations, Volume 2, the disposal part reads as follows:


"The reaction produces copious amounts of elemental iodine (I-2), which should be reduced to iodide ions before disposal.  To do so, carefully add 10g of sodium thiosulfate to each mixture and stir it until the mixture becomes colorless.  Caution! The reaction between iodine and thiosulfate is exothermic, and the mixture may become hot.  The cold solution should then be flushed down the drain with water."    


I've run this demonstration many times over the years and it's always a crowd pleaser.  You can also observe the absorbance profile of this reaction in a cuvette (without the starch) on a simple laboratory spectrophotometer and watch it eventually flat-line. 




Eric Clark, MS, CCHO, CHMM

Environmental & Occupational

Health & Safety Specialist

Los Angeles Trade Technical College




From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**PRINCETON.EDU> On Behalf Of Klotz, Ann
Sent: Friday, October 11, 2019 5:17 AM
Subject: Re: [DCHAS-L] Iodine clock reaction waste




Any drain disposal of chemicals should be evaluated by your local water authority. 




On Thu, Oct 10, 2019 at 11:49 AM Pam Auburn <aubu**At_Symbol_Here**> wrote:


I was wondering if anyone here has experience with this reaction and the proper waste disposal 


IO3- + 3 HSO3- --> I- + 3 SO4-2 + 3 H+

IO3- = 8 I- + 6 H+ --> 3 I3- + 3 H2O

I3- + HSO3- + H2O --> 3 I- + SO4-2 + 3 H+

2 I3- + starch --> starch-I5- complex (blue)



I saw from something published in 1996 "For disposal of waste products, combined all of the solutions used in this experiment with solid sodium thiosulfate until the mixture is no longer blue. The resulting clear mixture can then be discarded by flushing down the drain upon the addition of water."


Mitchell, R.S. Iodine Clock ReactionJ. Chem. Educ.1996, 73 (8), 783.


Is this still acceptable? 





Pamela Auburn, PhD

2041 Branard

Houston TX 77098

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Ann Klotz
School of Science
Siena College
515 Loudon Road
Loudonville, NY 12211-1462
Office Phone: 518-783-2402
Cell Phone 518-860-8489
Siena College is a learning community advancing the ideals of a liberal arts education, rooted in its identity as a Franciscan and Catholic institution.


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