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Chemistry: Hydrogen


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  • Type: Video Tutorial
  • Length: 13:42
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 147 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: Nonmetals and Hydrogen Introduction (2 lessons, $3.96)

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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Hydrogen is a tasteless, colorless, odorless gas at room temperature and what we are going to see is that it has not only commercial applications that are of extreme importance right now, but potentially extremely important uses in the future.
Hydrogen can be obtained from water, and that obviously constitutes an essentially endless supply. If you take water, you can electrolyze it into hydrogen and oxygen. The problem with this process is that it is very energy intensive. It costs a lot of energy to take water and split it into hydrogen and oxygen.
Now, it's a nice process, because the byproduct is oxygen and that is a good thing, and so it would be desirable to be able to carry this out. Scientists right now are trying to find a good way to effect this transformation using sunlight. Why would that be great? Well, we are bombarded each day with much more sunlight than we can use, and if we could just take even a fraction of that sunlight and convert it into splitting water into hydrogen and oxygen, that would allow us to store the energy of sunlight so that when the sun goes down, we'd have a very ready supply of non-polluting fuel.
Historically hydrogen was produced in very large quantities with reaction with reactive metals like iron and zinc. Jacque Charles for instance filled the first hydrogen balloon for lifting a person up off the ground by reacting just ungodly amounts of sulfuric acid with iron metal and he probably made the sulfuric acid by combustion of sulfur.
However, commercially, hydrogen is made by three processes. The first is reforming of natural gases and other hydrocarbons, methane, ethane, propane, of which I have illustrated methane here. So methane is fairly plentiful and, in fact, in some places it is so inconvenient to transport it, it's just burned off. Sometimes you will see these giant flames out in the middle of nowhere and that is just methane burning off. They very often build golf courses on top of dumps, and it turns out dumps out gas methane and so occasionally you will have flares pop up in the middle of golf courses.
If you react methane with water you can make carbon monoxide and hydrogen gas in a reaction that is called "reforming," and these are all in the gas phase, so that gives you a ready supply of hydrogen and then you can also apply a second reaction called the water gas shift reaction. In the water gas shift reaction you take the carbon monoxide out from the first reaction and react it with more water to form carbon dioxide, which is good, because carbon monoxide is toxic. Carbon dioxide, except for being a greenhouse gas, is relatively inert, and you make more hydrogen, so that is the water gas shift.
In the United States we have a tremendous amount of coal that we are not really tapping into. Part of the reason is that it is not economical right now to get at all the coal, but another problem is that the coal has a lot of sulfur in it, and the sulfur gives rise to, when you burn it, acid rain, but if you can do it in a plant where you can control everything and scrub for the sulfur that is a good thing. If you take coal and react it with water, you get carbon monoxide and hydrogen as well and this is something called the "water gas reaction." You can see that you can then take this carbon monoxide and plug into the water gas shift so that makes more hydrogen. Incidentally, this water gas shift reaction also happens to be the principle commercial supply for carbon dioxide, which is used to make things like dry ice and fizzy drinks.
Hydrogen comes in three isotopes. One with zero neutrons, one with one neutron and one with two neutrons and the great majority, more than 99% of all the hydrogen, has no neutron at all, so that is why when we talk about H+, we say that it is just a proton. The amount of H[2] that exists, when I say H[2] I mean two mass number, not two hydrogens, is .0156% and it has the common name of deuterium. There is a third isotope that has two neutrons, and we call that tritium and tritium is radioactive with a half-life of about 12.3 years it decays to form a helium three and an electron.
Now since it is radioactive it is does not constitute an isolable amount of tritium. In other words, if you take some water, by the time you try to get the tritium out of it, it would all be gone, that is a naturally occurring supply. So you can make tritium by the reaction of lithium[6] with a neutron to form a tritium in a helium[4]. Incidentally since the government is interested in making tritium because if there is going to be fusion at any point, we can go back and take a look at what fusion is, but fusion is the way the sun makes energy. One of the fusion reactions we are interested on the planet is to try to make a lot of energy as the fusion of deuterium and tritium, so you need to make a lot of tritium. Being that that is the case a lot of the naturally occurring lithium is being depleted of lithium[6]. Lithium occurs in two isotopes, six and seven, and so getting lithium[6]out from the lithium[7] is desirable, because you can make tritium out of it, and what that is doing is it is effecting the average molar mass of microscopic quantities of lithium. In other words if you go to the store and you buy some lithium it may not have the isotopic distribution that occurs in nature because somebody has gone through and sort of culled out some of the lithium[6]. Probably not even an issue for you.
It turns out that you can separate hydrogen from deuterium and one of the ways that you can do it is to take advantage of what is known as an isotope effect. What isotope effects are, are differences between two isotopes and for the great majority of the properties deuterium water, so D[2]0, and regular water, H[2]0, are largely indistinguishable, in other words they behave the same, they solubalize, sodium chloride, those sorts of things. They boil at roughly 100, and melt at roughly 0, but there are ever so slight differences. One of the differences is that D[2]0 boils about 101. You can take a look at the graphic box and compare their properties but because deuterium boils at a slightly higher temperature, that you gives you an opportunity to factually distill D[2]0 from H[2]0 and enrich it in D[2]0. Turns out that another isotope effect is that D[2]0 and things that have deuterium typically react more slowly, so it turns out that D[2]0 is probably toxic if you drank enough of it to replace all the water in your body with D[2]0 - replace all of the H[2]0 with D[2]0 then everything would go much more slowly, while that might not seem like a bad thing, it means that your enzymes would function more slowly, your brain would function more slowly, and everything would just go more slowly. So it is believed to be toxic, I don't know if they have actually ever done any experiments, certainly they have never done it with a person.
Hydrogen appears in many different compounds and I will just talk about the binary hydrides, of which you probably have heard of the two of the three classes. We have the three classes. We have the ionic hydrides so things like lithium hydride and sodium hydride and potassium hydrides and all the other alkali metals. Then calcium, strontium, and barium form hydrides as well. These things are alkaline, they are basic and they are actually reasonable reducing agents as well.
The metallic hydrides are actually metals that absorb differing amounts of hydrogen. So they retain their metallic properties, conductivity, and those sorts of things and another word for this would be an interstitial hydride, which is to say that hydrogen is so small it actually fits in the holes that occur in a typical metal lattice, and so titanium can pick some nonstoichiometric amount of hydrogen. Palladium can pick up some nonstoichiometric. I think I read somewhere that palladium can pick up a couple hundred times its volumes in hydrogen. Well why might this be important? If you wanted to store hydrogen, one of the ways that you could store hydrogen conceivably is to use a metal and have the hydrogen stored in this big chunk of metal. Again, going back to the first slide and making hydrogen from water, you have got to put the hydrogen somewhere and one of the places that you might store it would be in a metal.
Now this also turns out to be a problem, because what it does is it creates embrittlement. If you imagine that you have metal and this piece of metal is not absolutely perfect and there if are any discontinuities, any gaps in the metal, places where it is not absolutely perfect, the hydrogen is going to gravitate to those areas. What it does, it basically caps off the metal bond, so in other words instead of metal forming to another metal, if there is a dislocation or something like that, the hydrogen will actually gravitate to that site, and what happens is it weakens the metal. So this can both be advantageous if we can figure out how to control it but, the fact that metals absorb hydrogen can also be very disadvantageous because it does cause embrittlement.
The third class is the molecular hydrides of which we have talked about lots, methane, ammonia, those sorts of things, so I won't say anything more about that.
The commercial applications for H[2], for dihydrogen are three-fold, the first is that you can take carbon monoxide and react it with hydrogen to form methanol. You might say, "Well we just took methane and turned it into carbon monoxide and hydrogen. Why are we now taking that same carbon monoxide and hydrogen and turning into methanol?" The answer is that methane is relatively difficult to transport. It is a gas to very low temperatures. You can liquefy it, if you put it under very high pressure, being a gas at ambient pressure and temperature it is sort of difficult to transport. Not impossible, obviously we do it, but maybe not economical is the better way to say it. If you could turn it into methanol, methanol is a liquid at atmospheric pressure and standard temperature, and so what we do is we take methane and turn it into carbon monoxide and hydrogen and then we take the carbon monoxide and hydrogen and turn it into methanol. Methanol is very easy to transport, and you might know that methanol, I think, can be an octane enhancer, so that is one of the applications.
The really biggy is the Haber-Bosch process to make fertilizer because you can make ammonia from nitrogen and hydrogen and that is the basis for the entire fertilizer industry and that is what allows us to grow all the food that we grow. Ammonia is also the source of nitric acid as well. You can't go conveniently from N[2] to nitric acid. You can take ammonia and burn it and make nitric acid, so that is the two pieces of fertilizer, ammonium nitrate all comes from N[2], first by the reduction with hydrogen.
The third application for hydrogen is the hydrogenation, and you may have seen that word before. The hydrogenation of double bonds. So here we have ethylene and you can add hydrogen in the presence of a catalyst, something like nickel zero or palladium or platinum and you can add hydrogen across that double bond. Well where does that occur? You may have read on a label of food sometime, partially hydrogenated vegetable oil. Here is a schematic of vegetable oil. What we have here is we have a fat, and instead of a saturated fat, meaning no double bonds, we have fats that have double bonds in them and if you look at the graphic you will see that one of the things that these double bonds do is that they create kinks in the fat chain, so this is a glycerin molecule over here and you may want to review about fats and soaps. The point is that these kinks make these fatty chains not pack very well, and because they don't pack very well, this kind of a fat is typically not a solid, it is liquid. So unsaturated fats are liquids; that is, the way to remember. People tell well you should use olive oil instead of butter, the reason is that butter is a saturated fat, olive oil is a monounsaturated fat, for the most part. They are both mixtures. The site of an unsaturation and the double bond, is called the site of unsaturation, gives rise to more liquidy fats. Liquidy fats are great for your arteries, but they are not necessarily something to cook with. You may want to find an alternative for butter, and so the way that you make Crisco, which is that lard-looking thing, but it is made out of vegetables, vegetable oil, is that you fully hydrogenate these double bonds. Well partially hydrogenated, of course, means to hydrogenate some of the double bonds and it turns out that a catalyst for hydrogenation, or adding hydrogen across the double bond, can also be a catalyst for isomerization of the double bond if you take a look at the graphic you will see what isomerization of a double bond is. These are called sys double bonds and when they isomerize they become trans-double bonds. You may have heard the term trans-fatty acid, that is what we mean when we talk about a trans-fatty acid, is that it causes isomerization, which is a side reaction, undesirable side reaction, but that is what happens. So that is an important third use of dihydrogen in the food industry.
There is not a lot of hydrogen, and there is none free, sort of out there in nature because it being so low density just floats away, but we have reasonably good ways of making it. A significant problem is, that if you can make it from water that would be great, so if you want to go out and make a billion dollars. Figure out a good way to do that and the market is there waiting for you to make methanol or fertilizers or to hydrogenate fat, so a billion dollars if you can figure it out.
The Nonmetals
An Introduction and Hydrogen
Hydrogen Page [3 of 3]

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