WEBVTT

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[MUSIC PLAYING]

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JESSICA HARROP: Hi, I'm
Jessica and today I'm

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going to be talking about a
chemical demonstration called

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the Briggs-Rauscher Reaction.

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This reaction was discovered
by two San Francisco-area

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high school chemistry
teachers, Briggs and Rauscher,

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who were working
in a lab to come up

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with a visually striking way
to demonstrate an oscillating

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clock reaction,

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Let's watch MIT's Dr. John
Dolhun show us the reaction.

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Here he is at the
Cambridge Science Festival.

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JOHN DOLHUN: OK.

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So what I'm going to do is I'm
going to pour three colorless

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solutions into this beaker.

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Solution number one, and I'm
going to use kitchen chemistry,

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so I'm using my eye here.

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Let me just see.

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OK, there we are.

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Second solution.

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And the third solution.

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JESSICA HARROP:
So what happened?

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Dr. Dolhun mixed three clear,
colorless solutions together.

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The first solution
contains potassium

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iodate and sulfuric
acid dissolved in water.

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The second solution is malonic
acid and manganese sulfate

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monohydrate in water.

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And the third is hydrogen
peroxide in water.

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And when mixed together,
things get complicated.

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The overall reaction is this.

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So iodate, hydrogen
peroxide, malonic acid

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in the presence
of sulfuric acid,

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reacts to produce this
compound-- oxygen and water.

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But think about the
reaction this way.

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It's equivalent to saying
that metal and plastic react

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to produce a bicycle.

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In reality, there
are many steps that

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occur between those raw
materials and the finished

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result.

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And the Briggs-Rauscher
Reaction is similar.

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Here are the many
subreactions that

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occur to get from the
reactants to the products.

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What we see is a
cycle from colorless

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to amber to dark blue.

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And as these reactions
run, the relative amounts

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of the reactants
and the products

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dictate the color
of the solution.

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I2 is amber.

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I minus is colorless.

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And I3 minus is deep
blue when it interacts

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with starch in the solution.

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Triiodide is formed when
iodine and iodide interact.

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And this cycle continues until
all the reactants are used up.

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Hope you enjoyed the video
and I'll see you next time.

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