What Are Some Awesome Chemistry Demonstrations?

[mishima]

Hello,

I've been given 100% free access to a university chemistry stockroom to do chemistry demonstrations for intro students. I've already looked through a few books, such as Chemical Curiosities by Roesky and Mockel. I'm just curious what everyone thinks of when they think of awesome demonstrations. I want to be memorable.

 

[Bloodthunder]

What do you want to demonstrate specifically, like is there a topic you want to focus on? Or are you just asking about fun Chemistry experiments in general?

 

[Fra]

Except for everything that generates smoke and booms which is usually appreciated, how about something like the iodine clock.
http://en.wikipedia.org/wiki/Iodine_clock_reaction
It's very simple to do, as long as you can access the chemicals.

An introduction could first be to talk about chemical equilibrium, and second law. That usually chemical reactions then go a certain direction (to maximum entropy). (Maybe first show a simple iodine/starch complex, one way colour change)

Then show the iodine clock, and in the end ask them to think about how/if the oscillations are consistent with the second law of thermodynamics? You could even ask everyone to come up with an explantion own their on for the next class.

/Fredrik

 

[Fra]

See http://www.youtube.com/watch?v=LcHKWChwP58&feature=related

But of course one should have it on a stirplate to get a more distinct colour change.

/Fredrik

 

[mishima]

Bloodthunder-

I'm willing to go either way, but really just want to do something motivational...motivational to study chemistry I mean.

Fra-

That is definitely awesome, will look into setting that up. How long does it go?

 

[Fra]

I've done this along time ago and don't remember all details on the top of my head but the exact frequency and the time it lasts depends on concentrations.

But typically it keeps going for several minutes - just about right for a demonstration.

The idea is that the background discussion, should induce questions in the students, to make them ask what drives a reaction, and what the resolution to the apparent paradox of oscillating states is. To make it more mysterious I don't think you should reveal the answer directly, instead let them leave the demo scratching heads :)

I think good emphasis should be also on the introduction - before showing the iodine clock. If they do not understand the "normal" idea that a chemical reaction proceeds from an initial state to an equilibrium state of higher entropy and stays there, then they won't get the point of the experiment. They will just see a "oh a flashing bottle, cool". But to inspire them to learn chemistry make a short lecture first with a typical decay style equilibration, and give them a feeling that the understand that.

Then show the clock, and briefly mention the "apparent" paradox, then let them go scratch heads until next class. /Fredrik

 

[Bloodthunder]

Haha, I unfortunately just know most of the chemistry experiments that makes pretty lights or bangs.

Burning of ammonium dichromate
Colored Fire - http://en.wikipedia.org/wiki/Colored_fire
Elephant Toothpaste
http://www.youtube.com/watch?v=Nyzlt-dVgWQ&feature=fvwrel
Esterification?
Group I metals in water/acid?
Making fake blood - combining iron chloride with potassium thiocynate (made famous by fake stigmata)

I'll post more if I think of them.

I think the iodine clock reaction is boring. =P Unfortunately, it is also an important experiment for understanding reaction time.

 

[aroc91]

Oscillating reaction that cycles between colors.

Edit: Briggs-rauscher is what I was thinking of.

http://chemistry.about.com/cs/demonstrations/a/aa050204a.htm