DIY CHEMISTRY: Experiments with Manganese and some of its compounds.Lothar Graudins, Ph.D. John FlemingCOPYRIGHT 2009

IMPORTANT NOTE: THIS ARTICLE IS WRITTEN SOLELY FOR INFORMATIONAL INTEREST. IT IS INTENDED FOR THOSE INDIVIDUALS WITH AT LEAST ONE YEAR COLLEGE CHEMISTRY EXPERIENCE. NEVERTHELESS, WE CANNOT AND DO NOT ASSUME ANY RESPONSIBILITY WHATSOEVER FOR ANY MISUSE OR ACCIDENTS RELATED TO THE USE OF THIS INFORMATION.

In this age of specialization, we have many experts with only a partial knowledge of a subject. This is an outgrowth of an almost explosive development of new findings and research. Still, it's important to have at least a general overview of our subject. In this study of manganese, we will look at manganese ore, use an extraction process and end up with the actual metal. Finally, we will synthesize an important manganese compound. In the course of this process, you will find instructions for building a simple high temperature furnace capable of reaching 1,465 degrees Centigrade. This furnace will be useful not only in reducing Manganese (IV) Dioxide to Manganese (II) Oxide , but it will allow you to do many useful experiments where a high temperature is needed. Part of processing calls for obtaining the metal itself. This will be described using the Goldschmidt or Thermite process. From the metal, you will learn how to synthesize Potassium Permanganate using basic principles of electrochemistry. Two additional experiments are described: an important test for unsaturated bonds and a dramatic reaction illustrating Potassium Permanganate as a powerful oxidizing agent.

Major metals are found in the earths crust in complex forms called ores. They are mined by various industrial processes and subsequently purified. The chemistry student can often do some actual prospecting and mining as well as reclaiming of important material. This is a challenging and rewarding task. It is in this spirit that the procedure for processing manganese ore is presented. You could simply buy Manganese Dioxide as your starting point for these experiments. Manganese Dioxide is available from commercial supply houses such as a Ceramics dealer. On the other hand, there is some interesting bench chemistry not to be missed. In the case of Manganese, there are over a dozen ores. Among the richest are pyrolucite and braunite. I chose to start with braunite, since this is the ore I had easy access to. You can ask about mines in your state through the State Geological or Mining Association. Or, if you can't find this ore in a nearby mine, you can order it from a rock (mineral) dealer found on the Internet.

Braunite is a very dense, black material with a metallic luster. It is composed of manganese (approximately 60%) and silicates. Chemical processing allows us to extract manganese in the form of its chloride and, with further processing eventually obtain elemental manganese. The following extraction process relies on a analytical procedure. Although it may seem very elaborate and laborious, the process involves some interesting chemistry and promotes practical bench experience. If you are starting with braunite you must first obtain a coarse powder by running the ore through a rock crusher. If you are doing the chemical extraction process indoors, this definitely calls for a fume hood. Please read the detailed safety instructions at this point (see Addendum). It is most advisable to do this procedure outdoors. Incidentally, I find large coffee carafes and old tea servers made of Pyrex glass extremely useful. They are at least 500 ml capacity and usually come with handles. You can buy them cheaply in Thrift Stores. Whenever temporary storage of a cold liquid is needed, use drinking water bottles. Particularly in this process, since it is laborious to constantly clean flasks. Weigh out 100 grams of ore and place it in a 600 ml beaker. Cover it with 100 ml concentrated Hydrochloric Acid. Use commercial Muriatic Acid, which is a cheaper and impure form of Hydrochloric Acid. Repeated volumes of acid are added to the beaker, evaporating these additions until all of the ore is reacted. You can heat the mixture with a hotplate to speed evaporation but keep it below the boiling point, under 90 degrees C*. This process generates large amounts of chlorine gas. Chlorine gas is poisonous in larger concentrations. Use extreme caution when heating hydrochloric acid. Use gloves and a face shield. Expect copious fumes of acrid and toxic chlorine as well as hydrogen chloride. Do this outdoors or use a fume hood. The process is done step-wise because manganese ores vary in their composition. The braunite sample I processed required a total of 400 ml of Hydrochloric acid to completely react or digest the braunite. When this process is complete (or nearly so) you will notice an absence of reactivity upon further addition of acid. Also, there will only be a minimal amount of solid material left in the reaction vessel composed mainly of hydrated silica.

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When all of the ore has reacted, allow the mixture to cool to room temperature. If you wish to see crystals of manganese chloride, allow the mixture to stand for several days. Large, beautiful crystals will appear. (See Figure 1) below: While naturally pink to rose in color, these will usually be stained yellow due to the presence of iron. Notice the distinct shape of these crystals. Into which category of crystal structure do they belong? It may also have occurred to you by now that you have transformed a very solid rock into soluble crystals. At his stage, redissolve the crystals with additions of hot water. Save the solution and add it to the beaker. OR, if you have not allowed for crystal-

Figure 1. CRYSTALS OF MANGANESE CHLORIDE STAINED WITH IRON.

lization, add 400 ml water to the above cooled mixture. The insoluble silicates will now appear. This grainy material looks much like common sand (which most of it is!) Filter the solution. The manganese is present in your filtrate as Manganese Chloride. Discard the silicates. In order for the next step to work you must also have iron present in your solution. This is most often the case, as manganese ore contains iron ore as well. In my sample the intense yellow color was sufficient evidence. Nevertheless, if you have some Ammonium Thiocyanate (a common reagent for testing the presence of iron), make up a 10% solution and add a few drops to your filtrate. A deep red color appears in the presence of iron. ( See Figure 2). PAGE 3

FIGURE 2. THIOCYANATE TEST FOR IRON

The next step is to oxidize the Manganese Chloride to the oxide by using chlorine. Obtain some Calcium Hypochloride from a swimming pool supply store. This product is sold as a chlorinating agent under various brand names. Read the ingredient list and avoid the organic chlorides. Calcium Hypochloride (as a commercial product) is relatively stable and contains up to 50 % available chlorine. One important caution: Never add a granulated oxidizer directly to an acid. The reaction is violent and can easily cause injury. Remember also that chlorine gas is very poisonous in higher concentrations. Use a fume hood, face shield and gloves for this next procedure. Make a slurry of Calcium Hypochloride by adding 20 grams of the powder to 50 ml cold water. Use a 100 ml flask with a stopper. Shake well and slowly add this mixture (Calcium Hypochloride is only slightly soluble in water) to your cold acid mixture. You will notice bubbling and foaming as well as a black precipitate of Manganese Dioxide. PAGE 4

Slowly bring your mixture to a boil. You are converting Manganese Chloride to Manganese Dioxide. (Dont forget to use the fume hood!) You will see the mixture turn increasingly black as the Manganese Dioxide is formed. Boil for 20 minutes, cool and filter.** Extended boiling time results in larger crystals which is helpful during filtration. This is also a step-wise process. For my sample, I used about 500 grams of Calcium Hypochloride until the conversion was complete. Filtration is done with standard laboratory filter paper (such as Whatman #2), although ordinary coffee filters will work. The product is rinsed off the filter using a wash bottle filled with distilled water. You will obtain a clear yellow liquid. Test this filtrate for additional Manganese Chloride . Use a test tube with about 10 ml filtrate, add a few drops of the slurry. If you obtain more precipitate, repeat the above process. Finally the filtrate will become clear and no further Manganese Dioxide can be recovered. Dry the product and weigh it. What was your percent yield? My sample yielded about 30 %. What is likely to be your largest contaminant? Regardless of how you obtained your Manganese (IV) Dioxide, the next step is to convert it to Manganese (II) Oxide. This is done in a high temperature furnace that you can easily build. Manganese Oxide is most appropriate to a thermite reaction that produces raw manganese metal. The furnace uses a light-weight, easily shaped thermal brick with high insulating properties. In fact, the secret of obtaining very high temperatures (this furnace is capable of boiling ordinary salt, B.P. 1,413 C.) is adequate insulation. You use an ordinary propane torch for the heat source. (See Figure 3) The principle of adequate insulation is important to remember for any high temperature work you might consider.

FIGURE 3. A SIMPLE TORCH FURNACE CABABLE OF REACHING 1400 DEGREES CENTIGRADE

This type of brick is often available from larger hobby ceramic stores. You also can order the bricks from Thermal Ceramics posted on the Internet. Order Insulating Firebrick K-23. Although the recommended operating limit is 1260 degrees C, the bricks will not melt below 1510 C. I built a simple wooden frame to contain the bricks. Using a pocket knife, cut a cavity about 1/4 inch larger than the crucible. Cut a hole on one side of the crucible. Bring in the torch nozzle at a 45 degree angle. The idea is to allow the hot gasses to swirl around the crucible. (See Figure 3, above.) PAGE 6

Fill a crucible with the Manganese (IV) Dioxide you have produced. Heat at 800 C., a dull-red color, for 30 minutes in the above furnace. Your product will change color from black to a reddish tone. Repeat until you have converted about 100 grams to Manganese (II) Oxide. Mix this oxide with 25 grams aluminum powder. The balanced reaction or stoichiometric ratio calls for 212.7 grams MnO mixed with. 54 grams powdered aluminum. Below is the balanced equation: 3MnO + 2Al > 3 Mn + Al 2 O 3 As you can calculate from the atomic or molecular weights involved, 266.7 grams of the mixture theoretically yields 164.7 grams of manganese metal. Of course, life (and chemistry) are never that simple. Remember that you are starting with an impure product. In addition, there is significant loss due to vaporization at this high temperature as well as side-reactions whereby the Manganese (II) Oxide reverts back to the initial form. Finally, the slag or aluminum oxide entraps the metal. Nevertheless, you may be successful at the last step. If not, use pure Manganese (IV) Oxide as a starting point in the conversion procedure. Follow up with small increments of reactants going into the thermite mixture. The resulting mixture is known as Thermite aka the Goldschmitt process. In general, a thermite mixture results in a molten metal of an oxide that has been reduced by a highly reactive metal powder, usually aluminum or magnesium. Historically, iron oxide and aluminum powder was used to weld railroad track by actually allowing molten iron to fuse the ends. Thermite reactions produce extreme heat and light, molten metal splashings and hot sparks. If not carefully conducted, it is a dangerous reaction! To begin with, never exceed the recommended amount of reactants for a specific application. In this case, start with 125 grams of reactants. Also, important in this particular case, use only Manganese (II) Oxide. The dioxide produces flash powder, a violent reaction similar to igniting black powder. Never grind the combined ingredients. Always wear protective clothing and eye gear when using thermite or its ingredients. PAGE 7

To obtain a globule of manganese metal, prepare the reaction vessel. Use a small ceramic pot (flower pot) and place a crucible in the center of the pot after you have nearly filled it with sand. Surround the pot with sand. Also buy a ceramic dish for the pot. Drill a half-inch hole through the middle of the dish, to be used as a cover. (See Illustration 1 below).

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Be sure you do this outdoors only, in an area that contains no flammable material. Place the thermite powder in the crucible. Cover with the lid. Ignition is done with a piece of magnesium ribbon or a sparkler. A welding torch can be used if neither of the above is available. However, be extra careful with a welding torch to avoid overheating the mixture. Remember you are dealing with molten metal. This reaction typically sprays molten droplets, so allow for a large perimeter. Once the reaction is completed, wait at least 20 minutes. Using insulated gloves, empty the contents of the crucible and carefully sift through the material. You will find small metallic globules of manganese, usually trapped in a matrix of aluminum oxide. This condition can be improved upon by first heating the reaction vessel and adding reactants step-wise. But, in fact, for now, you only need a small nodule. The next portion of these experiments calls for synthesizing some Potassium Permanganate from a metal globule. Potassium Permanganate is a powerful oxidizer commonly used as a disinfectant and in water treatment. It is also used in analytical chemistry when a powerful oxidizer is needed. The usual synthesis calls for fusing manganese dioxide with potassium hydroxide in the presence of an oxidizer such as potassium nitrate or chlorate. However, it is very instructive to use a method employing electrochemistry. At this point you might review basic electrochemistry. In this experiment we prepare the permanganate by anode oxidation of manganese metal. Using a 600ml beaker, prepare about 300 ml of a saturated solution of Potassium Carbonate. This is done by stirring small amounts of Potassium Carbonate into 300ml of cold water (room temperature) until no more will dissolve. Let the beaker stand for 10 minutes until the solution is clear. The anode (positive terminal) and the cathode are simple iron wires. Connect the cathode to a power supply, which can be a set of DC batteries adding up to 6 Volts. I used a Regulated power supply with a DC voltage of 3.5 V and .15 amps. The anode is also an iron wire, with one end wrapped around the nodule. Immediately after introducing current, you will see a plume of violet permanganate drifting off the anode. Run the experiment for about hour to get a reasonably concentrated solution of potassium permanganate. See Figure 4 below. PAGE 9

FIGURE 4. ELECTROLYSIS OF MANGANESE METAL IN A SOLUTION OF POTASSIUM CARBONATE.

Using the above solution of potassium permanganate, you can now test for organic unsaturated bonds. Compounds containing unsaturated bonds will discolor the purple solution producing a brown, peach colored precipitate of manganese dioxide. You will learn more about unsaturated bonds in your study of organic chemistry. Unsaturation refers to a compound where double carbon-to-carbon chemical bonds are readily available for uptake of new constituents. Common vegetable oils are composed of fatty acid esters that contain unsaturated carbon bonds. When these bonds are altered, the permanganate is reduced and becomes colorless. Fill a test tube half-way with the solution you have just prepared. Now add about 2ml of a vegetable oil, such as Canola Harvest brand. Stopper tube and shake well. A color change to neutral or faint brown can be observed. If you perform this test with a more concentrated permanganate solution, you will find a very fine precipitate of manganese dioxide at the bottom of your container. You've come full circle. PAGE 10

Finally, the powerful oxidizing action of potassium permanganate can be shown in a dramatic reaction. For this experiment you will need about 20 grams of pure potassium permanganate. Place this amount in a small crucible. DO THIS EXPERIMENT OUTDOORS ONLY, AWAY FROM ALL FLAMMABLE MATERIALS. Quickly add about 5ml of glycerine to the crucible and stand back. A violent reaction ensues, with smoke and fire, as the glycerin is oxidized.

* You can use an ordinary thermometer. However, a better method is to use a thermocouple within a thin glass tube or sleeve. Use a little silicone oil for better heat transfer. This device is not only more accurate, but, more importantly for this experiment, easy to read. **If you do much filtration, you will want to invest in a suction filter and vacuum pump. For this work, due to Hydrochloric Acid fumes, you need a pump consisting of non-metal parts. Or, alternately, you can use a simple aspirator driven by water or compressed air. Compressed air devices are available from Auto Supply houses at low cost. These devices achieve a respectable vacuum and make short work of filtration. (See Figure 4) below:

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FIGURE 4. RIGHT ANGLE VALVE FOR GARDEN HOSE JOINED TO LAB WATER ASPIRATOR.

Advanced Topics and Experiments: 1. Ammonium Thiocyanate forms a deeply red and soluble complex in the presence of iron. Use a separatory funnel and extract it with ethyl ether. Crystallize the remaining Manganese Chloride. 2. Use a analytical chemistry flow chart to separate iron from manganese. You will probably need a pH controlled solution. PAGE 12

Addendum: A word about safety 1. For all procedures, closely follow instructions. If you are not clear about a particular step, do the research to find out. 2. Always stick to recommended amounts of reagents. Usually very small amounts are all thats necessary to complete an experiment. 3. Use protective gear such as gloves, safety glasses or a face shield. 4. Many experiments call for a fume hood or outdoor environment. Dont compromise this safety rule. 5. Never taste a chemical or solution. Most are highly toxic. If you spill a chemical or come in contact with a corrosive agent, immediately wash with plenty of cold water. Read the MSDS sheets on all chemicals you plan to use. 6. Learn about and practice safe disposal of all reagents. While most chemicals are not inherently dangerous, careless use can result in risky situations and harmful consequences. As in all aspects of your life, you must assume complete responsibility for what you do. In that respect, we, the authors, are not responsible for any accident, injury or mishap resulting from the information given in this article. There is no

mandate or recommendation that you do any of the procedures. That part is entirely up to you. The aboveexperiments may be hazardous for the novice. We recommend at least one year of college chemistry experience. PAGE 13

If you are under 18 and/or have no experience with chemical experimentation, you should choose less hazardous tasks and always ask for supervision. Most practices of applied chemistry, experimental rocketry, for example, have excellent to near-perfect safety records. This comes from intelligent and methodical work. If you enjoy high risk behavior, chemistry is not for you. Try skateboarding, motorcycle racing or even the celebrated Running of the Bulls in Spain.

GRAUDINS AND FLEMING COPYRIGHT 2009

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