chemistry

Old Nassau reaction

Old Nassau reaction is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Old Nassau reaction rather than just read about it. In short: The Old Nassau reaction or Halloween reaction is a chemical clock reaction in which a clear solution turns orange and then black. This reaction was discovered by two undergraduate students at Princeton University researching the inhibition of the iodine clock reaction (or Landolt reaction) by Hg2+, resulting in the formation of orange HgI2.

Key takeaways

Old Nassau reaction belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Old Nassau reaction to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Old Nassau reaction from memory before moving on to harder problems.

Reference excerpt

The Old Nassau reaction or Halloween reaction is a chemical clock reaction in which a clear solution turns orange and then black. This reaction was discovered by two undergraduate students at Princeton University researching the inhibition of the iodine clock reaction (or Landolt reaction) by Hg2+, resulting in the formation of orange HgI2. 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:

Na2S2O5 + H2O → 2 NaHSO3 IO3− + 3 HSO3− → I− + 3 SO42− + 3 H+ This reaction reduces iodate ions to iodide ions. Hg2+ + 2 I− → HgI2 Orange mercury iodide solid is precipitated until the mercury is used up. IO3− + 5 I− + 6 H+ → 3 I2 + 3 H2O The excess I− and IO3− undergo the iodide-iodate reaction I2 + starch → a blue/black complex A blue/black starch-iodine complex is formed.

See also Iodine clock reaction

References Alyea, Hubert N. (1977). "The Old Nassau reaction". Journal of Chemical Education. 54 (3): 167. Bibcode:1977JChEd..54..167A. doi:10.1021/ed054p167.2. "Simulation und praktische Durchführung der "Old Nassau" Uhr-Reaktion" (PDF). Archived from the original (PDF) on 2011-07-07. Lambert, Jack L.; Fina, Gary T. (1984). "Iodine clock reaction mechanisms". Journal of Chemical Education. 61 (12): 1037. Bibcode:1984JChEd..61.1037L. doi:10.1021/ed061p1037. "Old Nassau - Halloween Reaction". Huber, Hanspeter (1979). "Simulation of the Old Nassau Reaction". Journal of Chemical Education. 56 (5): 320. Bibcode:1979JChEd..56..320H. doi:10.1021/ed056p320. Fortman, John J. (1992). "The old Nassau demonstration: Educational and entertaining variations". Journal of Chemical Education. 69 (3): 236. Bibcode:1992JChEd..69..236F. doi:10.1021/ed069p236. Peter Keusch. "Cocktail 'Old Nassau' - Modifizierte Landolt Reaktion". Moss, Arthur (1978). "The Landolt, "Old Nassau", and variant reactions". Journal of Chemical Education. 55 (4): 244. Bibcode:1978JChEd..55Q.244M. doi:10.1021/ed055p244.2. Wilkinson, Lawrence E.; David Speckhard; James H. Maynard (2004). "Old Nassau Demonstration with Wilkinson Modification". Journal of Chemical Education. 81 (10): 1474. Bibcode:2004JChEd..81.1474W. doi:10.1021/ed081p1474. Moss, Arthur (1978). "The Landolt, "Old Nassau", and variant reactions". Journal of Chemical Education. 55 (4): 244. Bibcode:1978JChEd..55Q.244M. doi:10.1021/ed055p244.2. Lambert, Jack L.; Fina, Gary T. (1984). "Iodine clock reaction mechanisms". Journal of Chemical Education. 61 (12): 1037. Bibcode:1984JChEd..61.1037L. doi:10.1021/ed061p1037. Autuori, Marcos Alberto; Brolo, Alexandre Guimaraes; Mateus, Alfredo Luis M. L. (1989). "The iodine clock reaction: A surprising variant". Journal of Chemical Education. 66 (10): 852. Bibcode:1989JChEd..66..852A. doi:10.1021/ed066p852.1.

Worked examples

Example 1 — a first encounter with Old Nassau reaction

Start with the simplest possible case. Write down what Old Nassau reaction claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Old Nassau reaction before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Old Nassau reaction ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Old Nassau reaction

In research: Old Nassau reaction appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Old Nassau reaction in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Old Nassau reaction is common in secondary-school and first-year university syllabi. It links to neighbouring topics Clock reactions, so understanding it makes those chapters shorter.
In everyday life: Look for Old Nassau reaction outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Old Nassau reaction in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Old Nassau reaction means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Old Nassau reaction out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Old Nassau reaction in simple terms?

Why does Old Nassau reaction matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Old Nassau reaction?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Old Nassau reaction.