The Old Nassau reaction or Halloween reaction is a chemical
clock reaction
A chemical clock (or clock reaction) is a complex mixture of reacting chemical compounds in which the onset of an observable property (discoloration or coloration) occurs after a predictable induction time due to the presence of clock species at a ...
in which a clear solution turns orange and then black. This reaction was discovered by two undergraduate students at
Princeton University
Princeton University is a private university, private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth, New Jersey, Elizabeth as the College of New Jersey, Princeton is the List of Colonial Colleges, fourth-oldest ins ...
researching the inhibition of the
iodine clock reaction
The iodine clock reaction is a classical chemical clock demonstration experiment to display chemical kinetics in action; it was discovered by Hans Heinrich Landolt in 1886. The iodine clock reaction exists in several variations, which each invol ...
(or Landolt reaction) by Hg
2+, resulting in the formation of orange HgI
2. Orange and black are the school colors of Princeton University, and "
Old Nassau" is a nickname for Princeton, named for its historic administration building, Nassau Hall.
Chemical equation
The reactions involved are as follows:
#Na
2S
2O
5 + H
2O → 2 NaHSO
3
#IO
3− + 3 HSO
3− → I
− + 3 SO
42− + 3 H
+ This reaction reduces iodate ions to iodide ions.
#Hg
2+ + 2 I
− → HgI
2 Orange mercury iodide solid is precipitated until the mercury is used up.
#IO
3− + 5 I
− + 6 H
+ → 3 I
2 + 3 H
2O
The excess I
− and IO
3− undergo the iodide-iodate reaction
#I
2 + starch → a blue/black complex
A blue/black starch-iodine complex is formed.
See also
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Iodine clock reaction
The iodine clock reaction is a classical chemical clock demonstration experiment to display chemical kinetics in action; it was discovered by Hans Heinrich Landolt in 1886. The iodine clock reaction exists in several variations, which each invol ...
References
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*{{cite journal , last1 = Autuori , first1 = Marcos Alberto , last2 = Brolo , first2 = Alexandre Guimaraes , last3 = Mateus , first3 = Alfredo Luis M. L. , title = The iodine clock reaction: A surprising variant , journal = Journal of Chemical Education , volume = 66 , pages = 852 , year = 1989 , doi = 10.1021/ed066p852.1, bibcode = 1989JChEd..66..852A
Chemical reactions