WEBVTT

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[THEME MUSIC]

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

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going to be talking about
a chemical demonstration I

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like to call, "Money to Burn."

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And chemist Dr.
Bassam Shakhashiri--

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here he is-- is actually going
to be showing us the demo.

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He's the president of the
American Chemical Society,

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and is performing this
demo right here at MIT.

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Let's see if he has
some money to burn.

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DR. BASSAM SHAKHASHIRI:
What I am going to do

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now is going to reach in here.

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I'm going to take
dollar bill, and I'm

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going to put it in the
flame just like that.

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[AWED GASPS]

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STUDENT: Whoa!

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DR. BASSAM SHAKHASHIRI:
Was that too fast?

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What we always do in science
is repeat the experiment,

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so I take out what looks
like a dollar bill,

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but it's not a real dollar bill.

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I bring it close to the flame.

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STUDENT: [INAUDIBLE].

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DR. BASSAM SHAKHASHIRI:
Disappears into thin air.

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It looks like magic, right?

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I love magic.

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Magic is engaging,
but not informative.

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JESSICA: How is that dollar
bill burning up so quickly?

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Well, it's actually
not a dollar bill.

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It's called flash
paper, and it's

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paper that has been treated
with chemicals to make it burn

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quickly and leave no ashes.

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Now, flash paper
has been nitrated.

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Practically, what that means
is that you soak the paper

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in a mixture of concentrated
nitric and sulfuric acids.

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The cellulose in the
paper then reacts

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with the acid to produce
nitrated cellulose and water.

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The reaction is this.

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So our nitric acid here
mixes with the cellulose.

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Now, this is actually
just one unit

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in the big polymer
that is cellulose.

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It's got lots of little units
of C6H10O5, so in this equation,

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I'm only writing one unit.

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And that's creating nitrated
cellulose and water.

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Now, the nitro group, the
NO2 is the reactive group,

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and it can be very
reactive depending

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on the molecule that it's in.

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You've no doubt heard
of nitroglycerin,

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which looks like this.

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It's an explosive liquid.

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Or TNT, which actually
stands for trinitrotoluene.

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It looks like this.

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So all of these molecules
have nitro groups in them,

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and it's the nitro,
or NO2, groups that

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make these molecules explosive.

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Now, let's watch what happens
when Dr. Shakhashiri tries

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this again, but this time,
with a real dollar bill.

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DR. BASSAM SHAKHASHIRI:
I'd like someone

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in the audience to let me
borrow from them a real $1 bill.

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Is there someone
in the audience who

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would let me--
who would trust me

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with a real $1
bill or a $5 bill?

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Steve, how about
a $20 bill, huh?

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You got a $20 bill?

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OK, here's $1 bill.

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It's a real $1 bill.

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You know what I'm going
to do with it, don't you?

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So I have a jar right here,
and I have, in this jar--

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what do you suppose--
what does this look like?

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I have a liquid.

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What does it look like?

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Looks like?

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STUDENT: [INAUDIBLE].

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DR. BASSAM SHAKHASHIRI:
Looks like water.

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The way we describe this
liquid is to say it's

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a clear and colorless liquid,
which is what water is.

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So I'm going to take
this liquid, and--

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so I want everybody to
see the jar right here.

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Get this out of the way.

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I'm going to take
the dollar bill.

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I'm going to soak it in this
clear and colorless liquid,

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which looks like water,
and I'm going to fish it

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out using those tongs.

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You see, it's dripping
like any wet object would.

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And then I'm going to
take it to the flame.

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Take a good look at
it, now, [? Judy. ?]

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It may be the last
time you see it.

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So here is the
dollar bill on fire.

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Or is it?

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[AWED GASPS]

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DR. BASSAM SHAKHASHIRI: But you
did see a flame, didn't you?

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STUDENT: Yes!

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DR. BASSAM SHAKHASHIRI:
So now, I ask you,

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can this liquid be water?

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STUDENT: No!

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DR. BASSAM SHAKHASHIRI:
You know from experience

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that water does not burn
under these conditions.

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Right?

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So I will tell you
what's in this jar.

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This clear and
colorless liquid is

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a mixture of rubbing alcohol
and water, isopropyl alcohol

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and water.

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You know also from experience
that when you burn alcohol,

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what color flame do you see?

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It's kind of bluish.

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You remember what color
flame you saw here?

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It was a little yellowish.

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Right?

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That's because we also added a
little bit of sodium chloride

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in there.

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The eye is more sensitive
to the yellow color

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than it is to the blue color,
so we added the sodium chloride

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to enhance the visibility
of what's going on.

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JESSICA: All right, so
what happened there?

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Dr. Shakhashiri soaked the
money in a solution of water,

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rubbing alcohol, and a
little bit of table salt.

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When he puts the money in
the flame, the alcohol burns,

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producing heat and light,
energy, and carbon dioxide

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and water.

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The reaction is this.

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There's our alcohol
reacting with oxygen,

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producing carbon dioxide,
water, and energy.

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So why doesn't the bill burn?

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If you have a beaker of
alcohol and light it on fire,

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it's just that very
top layer of alcohol

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and the gas above it that burns.

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The rest of the alcohol
in the beaker does not.

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So that's what's happening
with our dollar bill.

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Let's draw a dollar
bill right here.

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So the alcohol, ROH
could be any alcohol,

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is evaporating off the
bill, turning into a gas,

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and burning, so those are
the flames that you see.

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But remember that the
solution is 50% water.

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The water is evaporating much
less quickly than the alcohol,

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staying in the bill and
preventing the paper

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from burning.

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So that's one way to
hold onto your cash.

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Hope you enjoyed
"Money to Burn,"

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and I'll see you next time.

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[MUSIC PLAYING]

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