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Chemistry: Demo: Self-Inflating Hydrogen Balloons


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  • Type: Video Tutorial
  • Length: 3:35
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 38 MB
  • Posted: 07/14/2009

This lesson is part of the following series:

Chemistry: Full Course (303 lessons, $198.00)
Chemistry: Stoichiometry (11 lessons, $14.85)
Chemistry: Mass/Mole Relationship Problems (6 lessons, $7.92)

This lesson was selected from a broader, comprehensive course, Chemistry, taught by Professor Harman, Professor Yee, and Professor Sammakia. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers atoms, molecules and ions, stoichiometry, reactions in aqueous solutions, gases, thermochemistry, Modern Atomic Theory, electron configurations, periodicity, chemical bonding, molecular geometry, bonding theory, oxidation-reduction reactions, condensed phases, solution properties, kinetics, acids and bases, organic reactions, thermodynamics, nuclear chemistry, metals, nonmetals, biochemistry, organic chemistry, and more.

Dean Harman is a professor of chemistry at the University of Virginia, where he has been honored with several teaching awards. He heads Harman Research Group, which specializes in the novel organic transformations made possible by electron-rich metal centers such as Os(II), RE(I), AND W(0). He holds a Ph.D. from Stanford University.

Gordon Yee is an associate professor of chemistry at Virginia Tech in Blacksburg, VA. He received his Ph.D. from Stanford University and completed postdoctoral work at DuPont. A widely published author, Professor Yee studies molecule-based magnetism.

Tarek Sammakia is a Professor of Chemistry at the University of Colorado at Boulder where he teaches organic chemistry to undergraduate and graduate students. He received his Ph.D. from Yale University and carried out postdoctoral research at Harvard University. He has received several national awards for his work in synthetic and mechanistic organic chemistry.

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Here's a neat little demonstration that illustrates the principle of the limiting reagent. What we have are four identical Florence flasks. And attached to each glass we have an identical balloon, except for the colors. The colors don't signify anything. What we have in each Florence flask is of a mole of hydrochloric acid. It's 100 milliliters of 1 mole of hydrochloric acid, so of a mole. And inside of each balloon we have an amount of magnesium. And our amount of magnesium increases as we go from left to right. So in this one, there's of a mole of magnesium, and then in this one of a mole, in this one of a mole, and this one of a mole. And if you think back to the balanced reaction for magnesium and hydrochloric, it's . And so what's going to happen is when we mix magnesium and hydrochloric acid, these balloons are going to self-inflate. They're going to be filling up with hydrogen gas. And what may not be obvious, but if you go through the math, is that in the first two, the limiting reagent is the magnesium ribbon. And in particular, there's less magnesium in the one on the far left. So this balloon should be limited the most, and then this one next. The third one is the exact stoichiometric ratio. And then the fourth one, the limiting reagent is no longer the magnesium. Now we've excess magnesium. The limiting reagent has switched to being hydrochloric acid. Again, we have the exactly the same number of moles of hydrochloric acid in each one, but we're increasing the amount of magnesium ribbon in each one.
So let's go ahead and take a look at how that appears. All I'm doing is dumping the magnesium ribbon into the flasks. It doesn't matter that we do them all at the same time or anything like that. While this works its way out, I think I'm going to go get a snack.
Let me remind you of what we looked at here. We have the same amount of hydrochloric acid in each of the Florence flasks. We put differing and increasing amount of magnesium as we go from left to right. The limiting reagent in the first case was magnesium. We put in . of a mole, still magnesium is the limiting reagent, but you can see that because we put more magnesium, the second balloon is bigger. Remember we're collecting the hydrogen product and inflating balloons with it. The third one was exactly the stoichiometric ratio, so the magnesium should have all dissolved. There's still a little bit here, but it's essentially all gone. That gives the largest balloon. And then when we add even more magnesium now, hydrochloric acid is the limiting reagent, so the balloon doesn't get any bigger. But there's a considerable amount of excess magnesium ribbon in the bottom of the Florence flask. That's now excess reagent. The hydrochloric acid is the limiting reagent.
Solving Problems Involving Mass.Mole Relationships
CIA Demonstration: Self-Inflating Hydrogen Balloons Page [1 of 1]

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