| Sulfur (Cont.) | |
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| Tweet Topic Started: Jan 24 2013, 10:36 PM (162 Views) | |
| Vargouille | Jan 24 2013, 10:36 PM Post #1 |
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So, I did the thiosulfate experiment I mentioned previously, and I thought this would be a good place to put it. 20.02 g of Na2S2O3-5H2O (sodium thiosulfate pentahydrate) were added to 100 mL of water and heated until completely dissolved. 16.5 mL of ~10 M HCl (31.45% HCl solution) was measured out. Upon complete dissolution, the thiosulfate solution was taken off heating and the hydrochloric acid added in one portion. The solution turned yellow, likely due to colloidal sulfur, and while still adding the hydrochloric acid, it turned into a yellow suspension. A sulfurous smell was noted (likely due to SO2), and the reaction mixture was left to settle out. On the next day, the reaction mixture was clear, but cloudy, and the sulfur had collected in a hard mass at the bottom of the beaker. This was filtered and left to air-dry. Once dry, it was powdered, weighed, and bottled. The yield was 2.10 g, for an 81% yield. Possible causes for the reduction of yield are physical losses, despite standard quantitative transfer methods, such as sticking in the filter paper, and remaining in a colloidal state. At some point I'll scale this up, and do a video on it, since the state change is pretty cool. Thiosulfate and pool-grade acid are pretty cheap, after all. |
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| plante1999 | Jan 25 2013, 09:57 PM Post #2 |
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Administrator
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Glad it worked! 80% yield is good, I guess it would worth a large scale try. It might also be useful to do something with the unreacted SO2, maybe making sulphites? For sure it is a safer process than the one I use, but the ratio sulphur-reactant is low. The preparation is easy and can be scaled up easily tough. Thiosulphate is not OTC, but is quite cheap. Continue your good work. |
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| Vargouille | Jan 26 2013, 01:02 PM Post #3 |
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It *could* be OTC if you can find either a) a photography store, where it is used to fix photographic negatives and make them unreactive towards light, b) a pool supply store, where it is used to reduce excess "chlorine" in the water, or c) a store selling dyes, where it is used to reduce natural indigo into a water-soluble form. I ordered a pound of the stuff from an online version of option C. As for using the SO2 for something useful, I had thought about that, but I don't yet have the parts necessary (namely a rubber stopper to fit an erlenmeyer flask, 5mm borer, 5mm glass tubes, and 5mm i.d. plastic tubing), although they shouldn't be too difficult to get together. I could use it to splice into a V2O5-tube and use that to make sulfuric acid/oleum, but that's something I'll think about in the future. |
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| plante1999 | Jan 26 2013, 06:03 PM Post #4 |
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Yes it could be OTC, I would use Pt for SO2 oxidation, as Pt is efficient, the SO2 is very pure, and the Pt actually work, the V2O5 is more tricky. A pound is not bad, but to get good amount of product One would need few Kg of the thiosulphate. Rubber stopper... I guess it is quite easy to buy them online as well as plastic and glass tube. |
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| Vargouille | Feb 8 2013, 09:38 PM Post #5 |
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Well, I did it. 200 g of technical-grade anhydrous Na2S2O3 was added to a 1-L beaker with about 500 mL of distilled water and heating was applied to fully dissolve the thiosulfate. Once the thiosulfate was completely solvated, stirring commenced and a 250-mL separatory funnel was set up above the beaker and filled with 255 mL of 31.45% pool-grade HCl. A fan was set up to remove noxious gases and the acid added dropwise. After complete addition of the HCl, the stirring was stopped and replaced with the use of a stirbar, and the entire solution allowed to settle. The next day, it was filtered, and the filtrate put onto a hotplate and heating was applied for about an hour to no obvious end-point. This was allowed to settle out and was filtered the next day, and the resulting filtrate discarded. Both "fractions" were allowed to dry for several days, and then ground in a mortar-and-pestle, put into a container, and weighed. The yield for this procedure was 40.09 g for a nearly quantitative (99%) yield based on thiosulfate. EDIT: There is now a video to accompany. YouTube messed up the beginning and end bits, though. Edited by Vargouille, Feb 8 2013, 11:13 PM.
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