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Chemistry: The Alkali Metals

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  • Type: Video Tutorial
  • Length: 12:08
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 130 MB
  • Posted: 07/14/2009

This lesson is part of the following series:

Chemistry: Full Course (303 lessons, $198.00)
Chemistry: Chemistry of Metals (8 lessons, $13.86)
Chemistry: Physical and Chemical Metals Processes (4 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 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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Alkali metals are a whole lot of fun, so we're going to talk about them a bit here. Alkali metals are in the first column in the periodic table, not counting hydrogen. We have lithium, sodium, potassium, rubidium, cesium and francium. I've never seen francium. It's radioactive, so it's not really important. But the alkali metals have a lot in common, and the most important thing is that they all form 1 plus cations - they all have one valence electron - that's relatively easily lost. And so that explains a lot of their chemistry, a lot of their reactivity. And it turns out that alkali metals are also typically very soft. And to show you how soft they are, I have a piece of sodium here and I have a razor blade. Unfortunately, Thinkwell can't afford to buy safety razors so I have a double-edge razor blade here. But I'm going to take this piece of sodium and I'm going to, very easily, cut it in half and hopefully not cut my fingers using this double-edged razor blade.
Okay, so you can see that I've cut it in half just by pressing down on it with a razor blade. In fact, the alkali metals are so soft that - as you go down, they get softer and softer, such that cesium is almost a liquid at room temperature. So you always hear about mercury as being the only liquid metal. But in fact, cesium is practically a liquid and francium, if we could get a macroscopic quantity, probably is a liquid as well. In fact, I think it is known, and if you look in the graphic, you can see whether or not it really is a liquid at room temperature.
Now, we said that the 1 plus oxidation state is really important, and let's talk about specifics here. Lithium is isolated from spodumene, which is lithium aluminum silicate, and by a series of steps, it's converted to lithium carbonate. And lithium carbonate is actually important in medicine, because it's the drug that is used to treat manic-depressive disorder. And manic-depressive disorder, people go through periods where they're very excitable and can't get any sleep to periods in which they feel really depressed. As an aside, it was discovered that lithium could be used to treat manic-depressive disorder. People who were sick used to go to things like spas where they would drink mineral waters it would make them feel better. Lithium carbonate does occur in nature by itself. And, in particular, people who had gout would go to this spa. Gout is where you have these calcium deposits in your joints and they hurt really bad. Well, their gout wouldn't feel any better from drinking the waters at the spa, but their manic depressive disorder would get better from drinking the waters that had lithium carbonate in them. Anyway, that's an aside.
Lithium carbonate reacts with hydrochloric acid to form lithium chloride and lithium chloride is how we get into the metal. Now lithium chloride is relatively high melting - about 613° Celsius. But if we make a mixture of lithium chloride and potassium chloride - 55 percent lithium chloride, 45 percent potassium chloride - it melts at about 430° Celsius - much more manageable. And we can electrochemically electrolyze this solution. The lithium, as a molten salt, the lithium ion goes to lithium metal and then the chloride goes to chlorine. And so that's how we can make lithium metal.
Now lithium metal's most important use right now is in lithium batteries. Lithium has a very negative reduction potential, meaning that lithium metal is very reducing - it wants to donate an electron. And in particular, lithium batteries have lithium as the anode. That's where the oxidation occurs. Manganese dioxide is the cathode. And these batteries have a number of advantages. First of all, the voltage in one of these cells is about 3.0 volts compared to regular alkaline battery, which is about 1.5 volts. So there's greater voltage in a lithium battery. But the other thing is, lithium is very lightweight, so the mass of a lithium battery that gets you this amount of voltage is typically very small. And then finally, they don't discharge spontaneously. They don't leak. And so they have a very long shelf life as well. So you buy a lithium battery, you can leave it on your shelf for a while and it doesn't do anything.
Now one of the things that lithium hydroxide does is that it gloms onto carbon dioxide to form lithium bicarbonate. And you might say what's so interesting about that? In fact sodium does exactly the same thing and potassium does exactly the same thing. But if you're building a space shuttle or you're building a rocket that you're going to put people in, people exhale carbon dioxide. And you want some machinery that's going to suck up the carbon dioxide, because when the carbon dioxide level gets too high, people start not thinking straight and ultimately, it kills them. You may remember the scene in Apollo XIII where the carbon dioxide level in the capsule was getting too high. Well, that was a lithium hydroxide scrubber that was doing this reaction. Why would you use lithium instead of sodium? Because the formula weight's almost half of what the sodium hydroxide formula weight is. When you're worried about taking stuff up into space, heavy is bad, light is good. And so that's why lithium hydroxide is used in space shuttles and in rockets.
Okay, next down in the periodic table is sodium. And sodium is prepared by electrolysis of molten sodium chloride, which comes from the ocean. Sodium metal reacts with water, just like lithium does, to form sodium hydroxide and hydrogen gas. And it reacts with oxygen to form sodium peroxide, which is Na[2]O[2]. And it also forms sodium oxide as well, but it's mostly this peroxide.
Now, sodium is really important and one of the forms is sodium hydroxide, which results from the electrolysis of sodium chloride in aqueous solution. You make hydrogen, which is useful, for reducing agents. You make chlorine, which is useful for making bleach, and you make sodium hydroxide. And sodium hydroxide is sort of a good plentiful cheap base. So it's used in aluminum purification. We talked about how you take aluminum oxide and you dissolve it and sodium hydroxide to form the complex ion, tetrahydroxylaluminate. And that's part of the purification. It's also used in drain cleaner. So if you look at the first ingredient in solid Crystal Drano drain cleaner, sodium hydroxide. It's good for hydrolyzing fats and things like that. And in particular, that's what goes on in soap making. So in soap making, we take something called the fatty acid. This is the way fats appear in nature, and you react them with a cheap base, like sodium hydroxide. And you make a glycerin molecule and you can make a sodium carboxylate salt. And this thing is what soap is. So for instance, if r is this really long chain, hydrocarbon, that has 17 carbons in it, then this is stearic acid. So this is stearic acid. And we make the sodium salt of stearic acid, and that turns out to be a soap. And the reason why it's a soap is that what we have is a very long polar chain and then an ionic piece that's soluble in water. Palmitate is from palm oil. And what these things represent, these soaps, is a fatty chain that's non-polar that surrounds the oil, plus this carboxylic acid - or carboxylate n group that's soluble in water. And so soaps can solubilize oils in water. So the water's out here. Oil doesn't like water, but by having this amphufilic piece that is non-polar, and then a charged piece, you can solubilize oil. And that's probably one of the bigger applications of sodium hydroxide.
But sodium is also useful in sodium carbonate and sodium bicarbonate. You already know sodium bicarbonate is baking soda, used in cooking. And sodium carbonate has the old-fashioned name "soda ash". Soda ash is useful in making glass. You take soda ash and silicon dioxide and lime and you make glass. And calcium carbonate is useful in water softeners. So calcium ions in solution are what precipitate out the soap. So when you have calcium ions in the presence of these sorts of species, it precipitates, and that's what a bathtub ring is. It's calcium stearate. It's calcium precipitating out this stuff. Well this stuff precipitates. It's not there to clean. And so, instead, what your water softener does is it exchanged the calcium ions for sodium ions. It makes calcium carbonate in the water purifier and that precipitates out so it doesn't make it all the way into your bathtub and so your soap cleans better.
Now, potassium is really important for a reason that sodium isn't and that is it's used in a fertilizer. You may have heard of NPK. NPK stands for nitrogen, phosphorus, potassium. And so a 10/10/10 fertilizer is 10 percent nitrogen, 10 percent phosphorus and 10 percent potassium, or 10 parts of nitrogen, 10 parts phosphorus, 10 parts potassium. The point is there's some distribution of those three ingredients that are common to fertilizers. Now potassium also does basically what sodium does. So you can make potassium stearate instead of sodium stearate. That's often in liquid soaps. Potassium metal is prepared from potassium chloride, not by electrolysis the way sodium and lithium are, but rather by reduction with sodium metals, so the red reaction here. And then what drives it is the fact that potassium is more volatile than sodium. And so at the temperatures at which this reaction is done, potassium is a gas, so it distills out of the mixture and that makes it work well. Potassium reacts with water to form potassium hydroxide in hydrogen. I'm going to show you that in a second. But potassium also reacts with oxygen to form potassium superoxide. Superoxide is O[2] single minus. And this is used in self-contained breathing apparatuses. Emergency breathing for a fireman walking into a fire has a self-contained breathing apparatus. This is the magic material. And what makes it magic is that it reacts with carbon dioxide and water to form potassium bicarbonate, which is inert and innocuous, and O[2]. Well, the carbon dioxide and water come from when you exhale. When you exhale, these come out and then when you inhale - or they react with the potassium superoxide. And then when you inhale, there's oxygen air ready for you to go. Now I wanted to show you the reaction of potassium and water to form hydroxide and hydrogen, and the reason is - it's pretty interesting; it's rather dramatic.
There's a story behind this and that is there's an episode of MacGyver, which starred Richard Dean Anderson, in which he's trying to make his way to the bottom of a Russian missile silo because there's been a earthquake and the control room computer thinks that there's been a nuclear attack and so it's about to automatically launch the nuclear missiles, and so he has to get all the way through. And he eventually gets to a point where there's a concrete wall and he can't get through the concrete because it's 10 feet thick or something like that. But he discovers that he's in a chemistry lab. So he says, well, let's look around. And he finds some potassium. So this is potassium. It looks a lot like the sodium. It might be hard to see. Let's put it in a dish and see if that helps. It's just sort of a shiny solid. It's also similarly very soft. And he takes a piece about this big. He also takes a gelcap, what drugs come in, and he takes the gelcap and he puts this blob of potassium inside the gel cap and he says, "Okay, stand back." And he takes the piece of potassium in the gel cap and he throws it into water and, kaboom, there's suddenly a 4-foot wide hole that's blown in this concrete wall. Well, that's nice.
Okay, so the point of that is if he did exactly what he said, we wouldn't get a hole blown in a concrete wall. What we'd get is a few sparks and a little bit of smoke. The message is that sometimes MacGyver used some real science when he's doing his tricks. And sometimes he's just full of [cuckoo sound].
The summary of all of this is that the alkali metals behave very similarly. They appear in the same column in the periodic table and they form 1 plus cations. Over and over I've shown you 1 plus cations. I've shown you over and over that they form the metal from the metal chloride by reduction and that the reactions with oxygen and water are very similar and finally that they are useful in a lot of industrial processes and industrial applications, like soap, like water softening and also medicinal applications, like lithium carbonate.
Chemistry of Metals
Physical and Chemical Processes of Metals
Alkali Metals Page [3 of 3]

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