Chemistry: Demo: Magnesium & Dry Ice

This lesson has not been reviewed.

Please purchase the lesson to review.

Magnesium is an extremely reducing metal and has the ability to give electrons to just about anything. And one of the things that it can give electrons to, believe it or not, is carbon dioxide. So it can reduce carbon dioxide. It can turn carbon dioxide all the way back to graphite and, in the process, the magnesium becomes magnesium oxide, MgO. And that's an example of a redox reaction.
I'm going to demonstrate that redox reaction right here. What I have is a block of dry ice with a pile of magnesium shavings on the inside. And I'm going to take this torch and I'm going to ignite the magnesium. What you're going to see at first is the magnesium burning in air, and it'll burn white-hot. Lots of special effects, for instance, oftentimes when somebody's trying to pretend that they are going to blow the lock, on the old Wild, Wild West, for instance. Jim West would always take something out of his pocket and stick in the lock of the jail and light it, and it would burn white-hot, and then suddenly the jail door would pop open. That was very often a piece of magnesium ribbon. Well, this is magnesium shavings, but the effect will be the same. You'll see a white-hot light. And then what I'm going to do is take this second piece of carbon dioxide, solid carbon dioxide - again, dry ice is solid carbon dioxide - and cover up the pile. And so, now the only source of oxygen that's available to the magnesium is going to be the oxygen that is in carbon dioxide. So what's going to happen is it's actually going to grab the oxygen out of carbon dioxide. Then, at the end, I'll show why we know that I say is going to happen really did happen.
All right, so all this stuff that's in the air is magnesium oxide, MgO, and it doesn't actually cause you to cough, so we won't worry about it. I once caused an entire building to be evacuated when I did this demonstration in a classroom. Somebody thought the building was on fire and pulled the fire alarm. Now, if you take a close look at this, you'll see a bunch of black stuff sitting on top of the white stuff. Well, the white stuff is magnesium oxide, MgO. It's a white solid. But right in the middle, there's also a bunch of black solid. And that black solid is graphitic carbon. So the carbon dioxide was actually converted into carbon and the oxygen was removed by the magnesium, and the magnesium then becomes magnesium oxide and the carbon dioxide goes all the way back to carbon. So it gets reduced all the way to carbon, and that's the evidence right here. You can see the black graphitic solid.
Stoichiometry
Chemical Equations
CIA Demonstration: Magnesium and Dry Ice Page [1 of 1]