(9 pm. – promoted by ek hornbeck)
Last time we started our discussion about sodium, and tonight we shall continue it. We have pretty much covered the quantum mechanical part and the properties and uses of elemental sodium, so tonight we shall focus on some of the compounds of that element.
Sodium compounds are extremely common and widespread, but not universally distributed. This is important for reasons to be seen later.
The most common sodium compound is common salt, or sodium chloride, NaCl. Everyone has personal experience with salt, both as a nutrient and as a melting aid for icy surfaces.
Sodium chloride occurs in mineral deposits (many of them from ancient, dried up seabed deposits), in seawater, and as the mineral halite, amongst other forms. Tremendous amounts are used in industry as a starting material or processing aid, in deicing operations, and only a little is used as food. One fascinating thing about salt is that it is the only rock that humans eat on a regular basis. It is also the only inorganic material to which humans have evolved specific taste receptors.
Salt is absolutely essential for mammalian (and much other) life. It serves several functions in the body. They are all important, so my ordering of these functions is arbitrary.
Sodium ions, along with potassium ions, serve to conduct electrical impulses in nerves. Without these ions we would surely die, and fast. Normally, within neurons potassium levels are higher than in the plasma, and sodium concentrations are lower. As a neuron fires, this situation is temporarily disturbed, but the equilibrium conditions are rapidly restored. If they were not, neurons would become irreversibly depolarized and thus unable to function again. Some neurotoxins operate by preventing the restoration of initial conditions.
Sodium, along with chloride, also are important for maintaining the osmotic balance betwixt cells and extracellular fluids. It the concentration of salt gets too high outside the cells, like in dehydration, the cells begin to lose water because of osmosis. Severe dehydration is a gradual thing, in general, and must be treated gently or those shrunken cells will absorb water too fast and burst, killing them. This is also why drinking seawater in quantity is deadly, since it has over three times more salt than plasma, increasing dehydration even though it is mostly water.
The deicing properties of salt are interesting insofar as how it works. Most people know that adding salt to ice makes the temperature decrease (the classic home example is making home made ice cream in a freezing device that is surrounded by an ice and salt mixture), but the connexion betwixt that and deicing roadways is often lost. Here is how it works.
A saturated solution of salt in water has a melting point of brine, saturated salt water, is zero degrees F (that is why Herr Docktor Fahrenheit used it as one of his reference points). If one puts salt onto ice, even though the initial interaction may be a solid/solid one (a slow process), as soon as a little salt is dissolved there become liquid domains, and solid/liquid interactions are much faster, especially since salt is quite soluble in water. Once that begins, the temperature of the ice/salt mixture begins to drop, but let us look at a typical example, perhaps where snow has covered a road at an ambient temperature of 20 degrees F.
The temperature of the ice/salt mixture drops, but since the roadway is warmer, heat is transferred to the mixture, raising it above zero degrees. As more salt becomes dissolved, more heat transfer occurs and finally the ice or snow just melts away as brine. There is one caveat: if the road temperature approaches zero degrees F, the process stops because there is no energetic driving force to transfer heat from the road to the ice/salt mixture. In extreme climates other materials that have lower freezing points than ice/salt ones are used. Now you know why ice and salt freezes ice cream in your home ice cream maker: the bucket containing the ice and salt is a pretty good insulator, but the metal one containing the goodies is an excellent conductor. Thus, the heat is extracted from the ice cream mix to the ice/salt mix and the ice cream freezes. Who would have thought that road salt and ice cream have so much in common! The other similarity is that rock salt, a rather crude but cheap material, is usually used for both.
Salt is also the starting material for many basic chemicals used industrially and in consumer products. Here are a couple of examples.
If one takes salt and mixes it with calcium chloride (to lower the melting point, otherwise it is inert) and makes that mixture the electrolyte in an electrolytic cell, properly designed, from one electrode one gets sodium hydroxide (lye) and from the other chlorine gas. We shall discuss chlorine another time, but sodium hydroxide is extremely important. Hydrogen is also produced, because to make it all work some hydrogen and oxygen have to be added, and that comes from the cheapest of all raw materials, water.
Sodium hydroxide is the archetypical base. It is extremely corrosive to most materials (hence the old name, caustic alkali or caustic soda) because it “wants” to abstract a hydrogen ion from anything that can give one to produce the very stable compound, water. So what are its uses?
Hundreds, if not thousands of uses exist for it. One that you touch every day is soap. This has been known since antiquity, but is well refined today. It turns out that if one takes the proper amounts of sodium hydroxide and fat, like animal fat or vegetable oil, reacts them with water and allows time to make its magic, instead of something that will burn you, the lye, or something that will just make you more greasy, soap is formed that not only will not burn, but also removes grease! I have written about that a long time before in this space, but have not the energy to find it now.
You used to be able to buy lye at the big box stores, but it is getting sort of hard to find because of meth cookers. The last time I looked it was available at Lowe’s, but the label did not say LYE on it, but rather DRAIN OPENER and you have to look at the label closely to see what you are getting. The liquid drain openers are concentrated sodium hydroxide solutions, many with thickening agents. You can get the “crystal” Drain-o at most stores, and it is mostly lye, but with the addition of some aluminum turnings. It turns out that sodium hydroxide gets very hot when dissolved in water (this is called a large, negative heat of solution), and that helps melt grease from plumbing. The sodium hydroxide solution reacts with the aluminum, releasing even more heat and hydrogen gas, which helps to dislodge clogs as well.
Sodium hydroxide is extremely corrosive to skin and especially eyes. It is hard to wash out concentrated solutions from the eyes before the cornea is destroyed, so handle it with extreme care. The reason that lye solutions feel soapy is that it literally making soap out of the lipids in your skin, doing damage at the same time. If you get a lye solution on you, vinegar or lemon juice is a specific treatment.
Another basic sodium chemical is sodium sulfate, Na2SO4. You see it mainly in powdered detergents and the use of it in detergents is waning because most liquid ones do not contain it. It is also used in the glass industry and in textiles. A really interesting use of it takes advantage of its relatively low (about 32 degrees C, just below body temperature) melting point. Since energy is released when it reverts to a solid, it is thus useful for storing heat in some solar heating schemes.
I used to use it in the laboratory to dry solutions of organic materials in organic solvents. At room temperature the stable form is the decahydrate, one sodium sulfate unit associated with ten water molecules. If the anhydrous kind is put into wet solutions of organic solvents (almost all organic solvents dissolve at least a little water, and ether around 10%), the sodium sulfate attracts the water and traps it in a solid, easily filtered out, mass. It has a further advantage of being pretty much inert to most organic substances, so solutions can be dried without degrading whatever material is being sought. Most sodium sulfate is produced my mining, but a fair amount used to come from the production of hydrochloric acid by reacting salt with sulfuric acid. Since both hydrogen and chlorine are produced by the same cells that produce sodium hydroxide, the bulk of hydrochloric acid now produced is made by burning the hydrogen in the chlorine, so the old process is not much used any longer.
One sodium compound that almost everyone has seen and touched is sodium bicarbonate, or baking soda, NaHCO3. It is only weakly basic, so it is not corrosive. Some of it is mined, but most of it on the market is produced from salt, carbon dioxide, water, and ammonia. The ammonia is regenerated at the end of the process and so is recycled, otherwise the process would be too expensive.
Sodium bicarbonate is used in cooking, mainly to produce carbon dioxide gas when baking cakes, biscuits, and other quick breads that are not risen with yeast. When mixed with some sort of acid, the carbon dioxide is released and the dough or batter rises. Buttermilk is the traditional acid, but in baking powders some solid acidic material is used so it does not react until being wetted. Usually a little less acid than required to neutralize the soda is added, because when it gets to around 70 degrees C it begins to evolve carbon dioxide even without acid. This property makes baking soda useful for putting out kitchen fires, particularly grease fires. Remember, NEVER use water on a grease fire. The best thing to do is just to put the lid on the flaming vessel, but if this is not possible, throw some soda on it. It decomposes so fast that it does not have time to cause the grease to splatter unless you use a whole lot and it can stay relatively cool in the middle of the mass, so do not throw a whole box into a deep fryer!
I neat trick to clean silver or copper of tarnish is to wash the item(s) thoroughly in detergent and water to remove dirt and grease, then put the items in either an uncoated aluminum pan or in any pan after first putting in a piece of aluminum foil. Add some baking soda and put the pan on the heat. This sets up a battery that electrolytically reduces the tarnish (copper or silver sulfide) back to the metal. This is preferable to silver polish because the polish removes the silver sulfide, whereas the soda method regenerates the silver. This is particularly important for silver plate since the plating is quite thin and repeated use of polishes will wear it away.
Baking soda is famous for being used in tooth cleaners, and it has real merit. It is a mild abrasive, but not so much that it damages tooth enamel, a mild antiseptic to kill bacteria, and a mild base that neutralizes the acids that bacteria produce that DO attack enamel. It is also a fair whitener. My grandmum used it (with a frizzled sweet gum stick as a toothbrush) until the she was around 50 or so and still had many of her natural teeth when she died at 101 and a half years!
The mild abrasive properties make soda great for cleaning items around the house without scratching them, but do not use it on really delicate items like laptop screens or lacquered surfaces. Also, do not use it on aluminum because it is basic enough to dissolve the protective oxide layer on aluminum. By the way, aluminum is so reactive that without this oxide layer (which forms immediately when aluminum is in contact with air) aluminum items would corrode away in minutes or weeks, depending on the size and geometry of the item. Aluminum foil would not exist with this protective layer, being destroyed by the air instantly. Remember, aluminum is produced by dissolving aluminum oxide in molten cryolite, sodium hexafluoroaluminate, a more basic and lower melting sodium salt. Sodium bicarbonate can not be used because it decomposes when it gets hot as mentioned earlier.
Many people use soda as an antacid, and for me it has no peer. Since I cut way back of fatty foods I rarely use it any more, when when I got heartburn half a teaspoon of soda in water would instantly, within 10 seconds, begin to give me relief. For those on sodium restricted diets it should not be used unless specifically directed by a medical professional. Alka-Seltzer is a combination of soda, citric acid, and aspirin. When the tablets are put into water, the citric acid reacts with the sodium bicarbonate to form carbon dioxide, water, and sodium citrate, itself a good antacid. Some of the aspirin also reacts with the soda to form sodium acetylsalicylate, a water soluble form of aspirin. That is why the aspirin gets into your system much faster than when taking tablets, because aspirin itself has a low water solubility.
Another common sodium compound is sodium carbonate, Na2CO3, or washing soda. It is present in almost all laundry detergents because it not only helps to soften water. It is also basic enough to saponify fat, turning it into soap and thus making fat water soluble. It is more basic than baking soda but not nearly as caustic as lye. Just do not get strong solutions in your eyes, but you CAN wash out washing soda solutions quickly enough to prevent corneal damage.
Sodium carbonate is used in enormous quantities as a raw material for glassmaking. Common glass is essentially a mixture of sodium carbonate, calcium oxide, and white sand, heated until it melts and then molded into glasses, bottles, and similar things, floated on molten tin to make window glass, or rolled into thicker plates for plate glass. All three of the raw materials are incredibly cheap, and that makes glass cheap as well. Now, there are hundreds of different glass formulations, but unless special properties are required, the soda lime glass is used because of its low cost. The next time you are at the hardware store look at the edge of a piece of window glass. You will see that it is quite green! That is because the glass is contaminated with trace amounts of iron, and iron in the 2+ oxidation state is green. The thin sections of the glass are too thin for the tint to be perceptible, but the edges of a piece a couple of feet wide are quite noticeable. For some applications even those traces are unacceptable so specially purified starting materials are used, increasing the cost of the glass considerably.
Another commonly used sodium compound is sodium borate, or borax, Na2B4O7. It is an excellent laundry booster and I use some in every load. It is also germicidal, and the former Mrs. Translator and I used it in the diaper pail to reduce odor of rinsed, soiled diapers. It is also an excellent and relatively nontoxic (to mammals) insecticide, and is safe to use around children and pets. People building or renovating houses are wise to put borax in the framing for drywall to act as a long lasting, nontoxic roach preventative.
Yet another commonly encountered sodium salt is monosodium glutamate, or MSG. This is used as a flavor enhancer in many salty and savory dishes. One of the reasons that soy sauce tastes like soy sauce is that soy beans are very high in the amino acid glutamic acid. As the protein is hydrolyzed, glutamic acid is released and combines with sodium, forming this material. Contrary to popular belief, real sensitivity to MSG is almost unknown and it IS a natural product. Almost any cheese has lots of it, except for unripened ones like cottage cheese and cream cheese. As a matter of fact, the scientific consensus is that MSG is the specific trigger for the fifth human taste umami (roughly translated from the Japanese as “delicious”). So go ahead and do not feel bad about using it. It really does make savory foods taste better, but works best with foods that are a little salty in the first place.
There are thousands of compounds with sodium in them, and we can only scratch the surface here. Therefore, we shall consider only one more.
Chlorine bleach is a water solution of sodium hypochlorite, NaClO. It is an oxidizing agent that is used to render colorless (and often water soluble) stains on fabric. It is made by reacting chlorine with sodium hydroxide, another product of the chloralkali process mentioned earlier. Bleach also contains a little sodium hydroxide to keep the pH high, because hypochlorite is unstable in neutral or acidic conditions, releasing chlorine. That is why it bleaches. When you add bleach to laundry, the pH decreases and chlorine, the real bleaching agent, is liberated. It is important to rinse garments thoroughly after using chlorine bleach because if the hydroxide is not removed it will damage the fabric. Weak bleach solutions are also excellent disinfecting solutions on hard surfaces that are not damaged by it.
Well, you have done it again! You have wasted many more einsteins of perfectly good photons reading this salty piece. And even though Huckabee realizes that making jokes about Chris Matthews wetting his pants when he reads me say it, I always learn much more than I could possibly hope to teach by writing this series, so please keep those comments, questions, corrections, and other feedback coming. Tips and recs are also always quite welcome. Remember, no science or technology issue is off topic here.
I shall stay around tonight for as comments warrant, since A***** is out of town. Tomorrow I shall return around 9:00 PM Easter for Review Time.
Doc, aka Dr. David W. Smith
Daily Kos, and