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
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
To: DCHAS-L**At_Symbol_Here**PRINCETON.EDU
Subject: Re: [DCHAS-L] Iodine clock reaction waste
Pamela,
Any drain disposal of chemicals should be evaluated by your local water authority.
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."
Is this still acceptable?
2041 Branard
Houston TX 77098
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