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Chemistry: Sulfur


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  • Type: Video Tutorial
  • Length: 10:45
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 116 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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Just as phosphorus is not a diatomic molecule in its own elemental form, sulfur is also not a diatomic molecule in its elemental form, despite the fact that the elements right above phosphorus and sulfur are diatomic molecules.
Sulfur prefers to form sigma bonds over pi bonds, so exists in its elemental form as small rings or chains in particular, S[8], which has the crown shape, that you can see in the graphic. S[6], S[20] and than something called plastic sulfur, which is obtained by taking elemental sulfur in its S[8] form and heating up above its melting temperature and then dripping it into water and then you can trap it into these polymeric SN strands.
Now sulfur actually exists in nature in its elemental form. You have probably encountered it if you have ever been to the hot springs for instance, Yellowstone. It is a yellowish solid, but it doesn't have a really strong smell. I will talk about what that really strong smell is, but it turns out that elemental sulfur doesn't smell really strongly. Like oxygen, it has the minus two-oxidation state, but a lot more compounds in which the sulfur is in a formal plus six-oxidation state as well. Its principle commercial applications are in vulcanizing rubber. What it does, is you take rubber, and you react it with sulfur and the sulfur cross links the rubber strands and that makes it goes from something that has the consistency of bubble gum to something that is the consistency of a more familiar rubber, something that you can make a tire out of. And then the other big application is the synthesis of sulfuric acid and more sulfuric acid is in made in the United States than anywhere else. Sulfuric acid is used in a wide variety of industrial processes, that I don't want to get into, but it has been said that the amount that a country produces, so the amount of sulfuric acid that a country produces is a reflection of its decree of industrialization. So if a country isn't making much sulfuric acid, it probably means that it doesn't have much industry.
Sulfur also appears in nature in a wide variety of sulfides, many of which we have talked about before. Mineral cinnabar, which mercuric sulfide, lead sulfide, which is known as the common name, galena. Iron sulfide S[2] is known as iron pyrite, also known as fool's gold. We talked about the sulfur sphalerite. Here is copper[1] sphalerite . A lot of the sulfur that is used in industry, doesn't come from elemental sulfur, it comes a byproduct of roasting these metals which is the first metallurgical step on the way to getting them as pure elements. So, for instance, if you take sphalerite and react it with oxygen and burn it oxygen essentially, you make zinc oxide, which is ready to be reduced so that's the second step in the metallurgical process of making zinc metals and a byproduct is SO[2]. Well decades ago, maybe even years ago, we just vented this SO[2] to the atmosphere and let it go, but SO[2] is a source of acid rain and so now days what companies are doing to avoid essential from the HPA is collecting this SO[2] and then rather than just dumping it as SO[2], they tie it up as calcium sulfides and things like that. But if you can take it onto sulfuric acid, then you can get money for something that you were previously just dumping.
The reactions that take SO[2] to sulfuric acid look like this. In general if you take sulfur and burn it in the presence of oxygen, you can make sulfur dioxide. Sulfur dioxide can be further oxidized only it is under more difficult conditions to sulfur trioxide and in industry it is oxidized in a V[2]O[5] catalyst, which is a vanadium five oxide and then sulfur trioxide reacts with water to form sulfuric acid. In fact, what really has to happen is that the sulfur trioxide reacts with sulfuric acid so that it is soluble in the sulfuric acid and it forms anhydrides of sulfuric acid and then those are hydrated to go back to sulfuric acid and you can see in the graphic that particular reaction.
Well so then if we are just venting sulfur dioxide to the air, it reacts with oxygen, maybe slowly, but eventually makes sulfur trioxide and then it goes on to sulfuric acid, alternatively sulfur dioxide reacts with water to form sulfuric acid. So these are both all examples of acid rain. In the northeast where they burn a lot of fuel oil and coal that is contaminated with sulfur, they make sulfuric acid, acid rain. I mentioned that before, in the west there is a lot more nitric acid, acid rain and that is because those come from burning nitrogen in the engine of your car, very accidentally, but it happens. Again, we are not obviously intentionally burning sulfur in the coal, it just happens to be there. As an aside, you may have heard of the term "sweet" referring to oil. Sweet, like British sweet, crude, that sweet refers to a low concentration of sulfur. If the oil has a low concentration of sulfur, then the refineries don't have to work so hard to get rid of the sulfur, so it is a higher quality of oil.
Now, the sulfur smell, or what we would normally associate with sulfur, the smell of rotten eggs, is actually not the sulfur, but hydrogen sulfide, H[2]S, it unlike water, so water is a liquid, hydrogen sulfide is a gas, it is very unlike water. First of all it is very poisonous. Its degree of poisonous is close to hydrocyanic acid, which you will recall we used to kill people in the gas chamber and it is also a relatively weak acid, smells really bad. And because it smells really bad, by the way, it's the smell we associate with rotten eggs. Organic chemists have used the fact that these sulfide molecules smell really bad to warn us that there is danger. So, for instance, they take things like dimethyl sulfide and methyl mercaptan and they put a little bit into a natural gas supply. So natural gas, methane has no smell, but when we add a little bit of one of these molecules in, it then has a smell. Why? Well, if you have a gas leak in your house and you can't smell the gas, you create an explosive situation and you don't even know it. Whereas, your nose turns out to be really sensitive to these sorts of compounds. These are very often associated with decaying flesh and stuff. And those are dangerous to you, they are pathogenic and so nature has a volatile point, where you have receptors in your nose that smell these kinds of things. So we take advantage of that to warn us when we have things like natural gas leaks.
Now, going the other way, oxidizing sulfur, again SO[2], sulfur dioxide, is used for sterilizing fruit, particularly dried fruit. When you get a package of dried fruit, it will usually say that it has been treated with sulfur dioxide. It's a fungicide; it also keeps the fruit looking fruit-like. If you buy dry fruit that hasn't been treated with sulfur dioxide, it looks brown. And sulfur dioxide dissolving in water gives you sulfurice acid and that this gives rise to bisulfite and sulfite. Lots of foods are treated with sulfite, sodium sulfite, and sodium sulsobisulfite. It acts as a preservative and keeps things from turn brown.
If we go look at SO[3], SO[3], sulfur trioxide, dissolves again to form sulfuric acid, which is a strong acid. The first association is essentially complete and even the second association is pretty signification. The KA for bisulfate is 1.2 x 10 to the minus two, so it is a pretty respectable weak acid. So these are salts, so sodium bisulfate is going to be an acid. It is a monoprotic acid and it is a solid, so that makes it really convenient. It is used in formulation for adjusting the PH in swimming pools and hot tubs and it is also found in things like toilet cleaners.
Now the last sulfur contain compound I want to talk about might be familiar to you if you are an amateur photographers or professional photographer. It is the thiosulfate anion. It is arrived at by taking sulfite and reacting with elemental sulfur to form thiosulfate. The prefix thio means sulfur, so regular sulfate would be SO[42] minus, and if you replace one of the oxygens with sulfur, you get to thiosulfate anion. So this reaction occurs in hot base and sodium thiosulfate. Thiosulfate that has been hydrated goes by the common name hypo or fix, if you are a photographer. And its role in the process is to dissolve silver bromide. So you know that silver bromide has relatively insoluble salt, what happens when you take a picture, first of all the unexposed film is silver bromide in a gelatin on some sort plastic sub straight, and when you expose it to light it makes silver metal and that silver bromide when it's reacted with a reducing agent, makes more silver metal and that creates the dark places on the piece of negative. But you want to dissolve away the silver bromide that want to be light, so that the light will go thru the film. And the way you do that, is that you show it thiosulfate and the thiosulfate reacts with the silver bromide that hasn't been exposed to light and it forms the complex ion with two thiosulfate and this is soluble in water so you an wash it away. So again the role is to dissolve the silver bromide that is unexposed and create the clear parts of the negative on your film.
So you probably coming into this lecture thought that sulfur was this really smelly stinky thing and I have dispelled that notion, but that smelly stinky thing is something that saves a lot of lives because we put it into natural gas and then you can smell and then you know if there is a gas leak. Then oxides of sulfur play a huge role in the preservation of food. Something that is important. Then finally, thiosulfate is important if you are a photographer. It allows you to make your negatives, both light and dark and that is the first step in making a print.
The Nonmetals
Group 16: Oxygen and Sulfur
Sulfur Page [1 of 2]

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