Saltpeter

Chemistry I Name___________________________ Section Beneath (and Beyond) Project Date ___________________________ The Extraction and Isolation of Saltpeter from Nitred Soil Brief History The first record of its preparation dates back to the 9th century in China, where alchemists – who had accidentally discovered it searching for the Elixir of Life – warned against mixing certain chemicals together. The particular mixture they were referring to consisted of charcoal, sulfur, and saltpeter. From there, word of it spread to Europe, where the English monk Roger Bacon made a detailed study of the concoction, eventually developing recipes similar to those used in certain pyrotechnic applications today. He wrote his recipes in cryptic anagrams, knowing full well the potential danger of what they could unleash: “Whoever will rewrite this will have a key which opens and no man shuts, and when he will shut, no man opens.” Unfortunately for Bacon, others were unable to unlock the secret of the preparation of this mixture and by the Middle Ages, it was becoming the central weapon of war, powering catapults, cannons, and, eventually, muskets. The concoction whose history was just briefly introduced is, of course, gunpowder or black powder. This low explosive (it only detonates when confined) is a mixture of three simple ingredients: (1) Charcoal, (2) sulfur, and (3) saltpeter or potassium nitrate. It is the third component of that mixture with which the present lab project is concerned. One of the challenges of creating a quality black powder is obtaining pure saltpeter. Throughout history, that has been accomplished in various ways. One of the earliest among these was its extraction from soil; later methods involved mining it from vast deposits in the arid Chilean desert and finally, most recently, its chemical preparation. You will be attempting to replicate the soil extraction method. In its original application, this process would begin by a taste test to determine if the earth in question would “. . . prick the tongue and taste like spice” (Clarke in The Natural History of Nitre), an indication that bacteria in the soil had con- verted other nitrogen compounds to nitrates. You will skip that step and move on to the real chemistry that this method involved: (1) Extracting the nitrates from the soil, (2) concentrating the nitrates in the extract, (3) converting the nitrates to their potassium compound, and (4) crystallizing that potassium nitrate. Additionally, you will perform chemical tests to verify that you have indeed isolated relatively pure saltpeter. Finally, you will combine your isolated product with that obtained by other groups and the class sample will be combined with the other two ingredients in black powder and tested. This will set the stage for an experimental investigation of a pyrotechnic effect for which black powder is necessary. Outline of the Experimental Work A. Extraction from the Soil 1. Goal: This Project begins with each group being given a single material by the instructor – a large (800-mL / 1 L) beaker filled with nitrate-enriched soil. In this section, it will be your group’s objective to find the cheapest and most efficient way to remove the nitrate salt from the soil, leaving the majority of other components behind. The only additional information you will be provided is that the main form of nitrate is the compound calcium nitrate [Ca(NO3)2] and that the other major components of the soil are organic compounds. 2. Follow-up Work: As part of the report you will provide by Project’s end, you are asked to. . . a.. . . describe [in detail] all of the steps of the process you used to isolate the nitrate salt and why you used the particular approach that you did. b.. . . identify what all of the chemical species are present in the final product that you end up with in this extraction step and how you know that they are present. B. Removing a Final Contaminant and Concentrating Your Extract 1. Goal: Completion of Part A. will leave you with your prized calcium nitrate product in whatever medium you used to extract it from the soil. This leaves you with a couple of technical problems. First, whatever medium you used probably also extracted a major component of soil known generally as humic acid; this must be removed from your extract. The hint that you will be provided in this arena is that humic acid is an organic material. There are often organic compounds in the water we drink; what do water filtration systems use to remove them? Once you have gotten rid of this last remaining contaminant, you will have isolated relatively pure calcium nitrate in your extract. The [second] problem is that there is most likely very little of your calcium nitrate in a very large amount of your extraction medium. As a result, it will be necessary for you to find a way to concentrate the extract. 2. Follow-up Work: As part of the report you will provide by Project’s end, you are asked to. . . a.. . . describe [in detail] all of the steps of the process you used to remove the organic contaminant and how you decided on this particular approach. b.. . . describe [in detail] how you concentrated the extract. c.. . . provide a simple definition for the term concentration. d.. . . replicate the pictures below on your report paper to illustrate what happened (at the microscopic level) in your product extract when you concentrated it (with Before representing a volume of the extract before the concentration process and After representing the same volume after concentrating the extract). ..

C. A Chemical Conversion 1. Goal: This is the most critical step of the process – and the one which will truly require you to put your knowledge of chemistry to work. Saltpeter goes by the chemical name potassium nitrate. ‘Nitred’ soil often contains two other nitrate compounds – sodium nitrate and calcium nitrate (your soil sample happens to be ‘enriched’ with calcium nitrate). Neither of those nitrates is effective for use in gunpowder. The challenge in this section is to chemically convert the other nitrate compound(s) to the potassium version. The one hint that will be given in this regard is that you will obviously need to perform some kind of replacement reaction. The simplest version of these is the single replacement reaction, which to accomplish the task at hand would require the addition of pure potassium metal to the concentrated extract sample you currently possess. The equation to represent the reaction that would take place would be. . . Calcium nitrate + Potassium Î Potassium nitrate + Calcium However, for reasons that you will be asked below, that is not a workable solution. This leads us to explore the second possibility, a double replacement reaction. For this particular conversion, it would take on the general form. . . Calcium nitrate + Potassium ? ? ? Î Potassium nitrate + Calcium ? ? ? Though this is a viable alternative (especially considering the nature of your extract sample and what typically occurs in this type of Rx), it presents you with a new problem: What potassium compound (salt) should you use? You will have to make your own choice in this regard from this list that appears below: a. Potassium acetate d. Potassium chromate b. Potassium carbonate e. Potassium hydroxide c. Potassium chloride f. Potassium iodide You should base this choice on the fact that once the potassium nitrate is generated by the double replacement reaction, you will need a way to separate it from the calcium compound that is also produced. The easiest way to achieve that separation is if one of the compounds is in one state (e.g. solid) and the other is in a different state (e.g. liquid). Once you have made your choice, present it to your instructor who will provide you with the appropriate materials. Finally, for this part of the work, you will need to separate the target compound (potassium nitrate) from the unwanted side product of the reaction (the calcium salt). You will have to design your own procedure for doing this. 2. Follow-up Work: As part of the report you will provide by Project’s end, you are asked to. . . a.. . . do some research and explain why neither sodium or calcium nitrate are effective compounds to use in gunpowder. b.. . . explain why the single replacement reaction involving simply adding pure potassium metal to your extract would not have been a good way to generate potassium nitrate. c.. . . explain why you chose the particular potassium salt from the list above that you did. d.. . . write a complete, balanced chemical equation for the reaction that you used to convert the calcium nitrate into potassium nitrate. e.. . . describe the procedure you used to separate the potassium nitrate from the calcium salt and what state the potassium nitrate is in following that separation. D. Crystallization and Determination of Product Purity 1. Goal: This is the part where you can sit back and allow nature to do most of the work. Following the work you completed in C., you will have a relatively pure sample of product dispersed in whatever medium you have used since back in A. The trick now is to concentrate the saltpeter in this medium and then allow the process of crystallization to proceed at its own sweet pace. You will be able to gain some insight into the purity of your product by observing the quality of the crystals once they form – particularly their shape. It would be useful to find a resource that describes the traditional shape of potassium nitrate crystals (for instance, salt crystals are cubic) and then compare the reference description to the shape of your crystals. A test of a physical property (such as crystal shape) is not nearly as convincing though (particularly since there are only about seven basic crystal structures) as some sort of chemical- property evidence. That being the case, you will be expected to gather such evidence. You know that your goal was to isolate potassium nitrate; the testing you conduct should prove that both parts (the metal / non-metal or + / -- halves) of that ionic compound are present in the crystals with which you end up. For the potassium half, you will be left on your own to devise a simple qualita- tive test for this ion based on work done previously in this class. For the nitrate half, a quantita- tive test should be conducted based on the following directions. . . a. Mass 0.10 g. of your isolated product and transfer the solid to a 1-L beaker. b. Measure 1000 mL of water and add it to the solid in the beaker; stir to dissolve. c. Obtain a nitrate test strip. Follow the directions on the test-strip bottle. Determine and record the ppm value for the nitrate concentration as determined by the strip.

2. Follow-up Work: As part of the report you will provide by Project’s end, you are asked to. . . a.. . . identify what crystal structure potassium nitrate is expected to have. Also, identify what crystal structure your final product had. b.. . . describe the test you devised to confirm potassium’s presence and the results of that test. c.. . . present the concentration value you determined for the nitrate using the test strip. Compare that to what the concentration value should have been based on the recipe you followed and given that 1 ppm = 1 mg (0.001 g.) dissolved in 1000 mL. E. The Exclamation Point 1. Goal: If you have made it this far [as a class], you deserve some type of reward for your efforts. That reward will be to pool the class’s product into a single sample of potassium nitrate, grind it into a powder, mass the powder and then use the equation below to determine how much charcoal and sulfur to combine with it to make a class batch of gunpowder. . . Carbon + Sulfur + Potassium nitrate Î Potassium sulfide + Carbon dioxide + Nitrogen 2. Follow-up Work: As part of the report you will provide by Project’s end, you are asked to. . . a.. . . write a complete, balanced [symbolic] equation based on the word equation given above. b.. . . show the calculation you used to determine the amounts of charcoal and sulfur and the results of those calculations. Experiment Resources 1. http://www.bbc.co.uk/history/games/gunpowder/index.shtml -- BBC game built around a plot to blow up a Catholic church 2. http://www.gabarin.com/ayh/Powder.htm -- Some really good history concerning the preparation of KNO3 including work done by the alchemists 3. http://www.blackpowdernet.com/ -- Title speaks for itself 4. http://en.wikipedia.org/wiki/Gunpowder -- An on-line encyclopedia reference 5. http://footguards.tripod.com/06ARTICLES/ART28_blackpowder.htm -- An interesting history of some of the recipes for making black powder 6. http://www.twilightbridge.com/hobbies/festivals/independence/historyfireworks.htm -- black powder related to fireworks 7. http://internet.cybermesa.com/~sam1/powder/bp.html -- very thorough information 8. http://www.jce.divched.org/Journal/Issues/2001/Dec/PlusSub/V78N12/p1609.pdf – JCE article (December 2001) on Humic Acids 9. http://www.grow.arizona.edu/water/waterquality/ppm.shtml – Animation showing ppm 10. http://www.waudesign.com/Milligrams_per_liter.htm – A simplified presentation of ppm