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Chemistry: Demo: Creating Acid Rain

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About this Lesson

  • Type: Video Tutorial
  • Length: 5:33
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 59 MB
  • Posted: 07/14/2009

This lesson is part of the following series:

Chemistry: Full Course (303 lessons, $198.00)
Chemistry: Nonmetals (12 lessons, $19.80)
Chemistry: Group 16: Oxygen and Sulfur (3 lessons, $4.95)

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 http://www.thinkwell.com/student/product/chemistry. 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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Thinkwell
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Earlier we made universal indicator by taking a cabbage and soaking it in water. The cabbage soaked in water gives a solution that's purple, and this is the color that the water has when it is essentially neutral, when the pH is very close to seven. We made this with de-ionized distilled water, so it makes sense that it should be really close to seven. But we also took that same universal indicator and we showed it some sodium hydroxide and it has this greenish yellow color and some baking soda, which is a wheat base and it has a blue color and then we showed it some vinegar, acetic acid, which is a weak acid and it has a pink color, and then we pretended to show it some stomach acid, which is hydrochloric acid and it turns this very intense red color.
So let's now play a little bit more with our universal indicator. What I did here is I have a beaker full of water, and this is Texas water, and Texas water has been exposed to limestone. The aquifer runs under slabs of limestone and so the water become alkaline as a result of being in equilibrium, maybe not total equilibrium, but at least in contact with the calcium carbonate, which is a base. And so you can see that, unlike water that's at pH[7] that would come from distilling the water, when we take just plain old tap water and put our indicator in it, it is blue. It is close to the color of the bicarbonate, and that sort of makes sense, because bicarbonate is a weak base and the calcium carbonate is going to be a weak base.
Now what I want to do, is I want to show you that we can make acid rain from carbon dioxide and water. People are always worried about acid rain. They are worried about the fact that it is poisoning lakes and it's killing the fish and stuff like that. But it turns out that natural rainwater, rainwater that is just in equilibrium with the carbon dioxide that is here - so way before humans were even on the planet, the rain was still acidic, and the reason why it is acidic is because water reacts with carbon dioxide to form carbonic acid, and that carbonic acid is a weak acid, and so rain is naturally acidic with pH of about 5.6. What we are worried about now is that because of the industrial revolution, and because we have been burning fossil fuels, we're making sulfuric acid and nitric acid, and those things are also in the rain, so they are making the rain significantly more acidic than 5.6. But the point is that rain is naturally acidic, as a result of the equilibrium between water and carbon dioxide.
And I am going to show that to you by adding solid carbon dioxide, which is something that we call dry ice, to my beaker of limestone, equilibrated water from Texas. I am actually going to cheat it a little bit more and I am going to add a little bit of sodium hydroxide, which is a strong base, and so we will see more color changes as we add our dry ice, as the dry ice comes into equilibrium with the water. So I have just added a little bit of base, and that is just going to make the water a little bluer. I wish I had something to stir with. Hang on, just like that. Okay that's good. Okay, so that's the color of the water with some strong base into it, and now I am going to take just a piece of dry ice, and this is something that you can do at home. Take a piece of dry ice and put it into the beaker and then we will watch the color changes.
And so the dry ice, remember is carbon dioxide, and so it is reacting with the water and you can see that the color is turning from green towards blue. So in other words, it is making the progression through these various colors of our universal indicator, and I will sweep away some of the carbon dioxide so maybe you can see that better. So it has gone from green to blue, and as it equilibrates with the water, it is making more carbonic acid and the more carbonic acid is decreasing the pH of this solution. Okay, so now it is moving into the purple regime, which is pH neutral, about pH[7], and then I think that we are going to be able to get all the way up into the pink, before it is essentially at equilibrium. That would be carbonic acid equaling with the water and it is not going to get anymore acidic because we don't have anything that can give rise to a strong acid. If we had nitric acid or we were bubbling SO[3] through this, then SO[3] remember, reacts with water to form sulfuric acid H[2]SO[4] and then we could get all the way to red, but for what we are trying to do, I think we are just going to barely get into the pink region. Which is some pH between what acidic acid is and what neutral water is.
So you can see that we are at least a little past the purple, and that is just about as far as we are going to go. What this indicates is that natural rainwater, which is water that is in equilibrium with the carbon dioxide that is in the air, is going to give rise to a slightly acidic solution. We have essentially made our own acid rain here. It is not the stuff that everyone is worried about, because it is just no as acidic as the nitric acid raid that's plaguing the Los Angeles and West Coast area, where it comes from burning fossil fuels in cars, like gasoline or in the Northeast, where the problem is sulfuric acid from burning coal, because coal has some sulfur in it and so we are making some oxides of sulfur in the Northeast.
So bottom line is from cabbage juice you can make your own universal indicator, go to the store, pickup a little bit of dry ice, you can make some acid rain for yourself.
The Nonmetals
Oxygen and Sulfur
CIA Demonstration: Creating Acid Rain Page [1 of 2]

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