May 14, 2011
I’ve known for a long time that I could easily obtain bismuth or bismuth alloys from environmentally-friendly replacements for lead shot used in hunting. However, it wasn’t until this past week when I got an awful stomach flu did I really start to think of bismuth as an interesting element for the amateur chemist. During this time, Pepto-Bismol, so named because its active ingredient is bismuth subsalicylate, became my best friend. It is amazing that this stuff, which was invented 110 years ago, works wonders for a bad case of the runs. But still to this day nobody seems to know why bismuth subsalicylate works so well! It’s thought to be beneficial because it is an antacid and can coat stuff in your intestines well, but I haven’t found a concrete explanation from my readings. While I was sick, I took the maximum allowable dose of the liquid formulation of Pepto-Bismol, which meant I consumed about 4.2 g of bismuth subsalicylate in one day. It was a bit frightening to subject my body to such high amounts of a heavy metal, especially since bismuth sits right between toxic lead and radioactive polonium on the periodic table! Nevertheless, I’m completely fine after having several grams of bismuth pass through me and so has everyone else who has taken Pepto-Bismol in the past century.
Lest you think I am a spokesperson for Proctor & Gamble, I better start in on some bismuth chemistry. Although it’s probably cheaper to obtain it from bismuth-based shot or solder, bismuth metal can be easily extracted from Pepto-Bismol. Hydrochloric acid will convert the bismuth subsalicylate into bismuth chloride. The solution can then be filtered, and aluminum can be used to precipitate out metallic bismuth. To separate the bismuth from aluminum impurities, the mixture of metals could be reacted with HCl. HCl will react more vigorously with the aluminum than it will with the bismuth, leaving behind relatively pure bismuth which can filtered.
I have a few uses for elemental bismuth in mind. First, I’d like to make some bismuth and bismuth oxide crystals which can be beautifully colored. Second, bismuth has a relatively low melting point of 272°C, thus making it an easy metal to cast. Interestingly, unlike most metals, it becomes less dense upon melting so you can add this to other metals to make alloys that don’t expand or contract at all during casting.
So with a whole lot of cheap bismuth metal in hand, it would be time to make some interesting bismuth compounds. Bismuth(III) nitrate would be a good starting point since, as a pentahydrate, it is one of the less moisture sensitive Bi3+ salts. It would be formed by reacting nitric acid with bismuth metal.
2Bi + 6HNO3 --> 2Bi(NO3)3 + 3H2
Bi3+ is very acidic in aqueous solutions because upon addition of Bi(III) salts to water, insoluble compounds containing the bismuthyl ion, BiO+ are usually formed. Thus, bismuth nitrate gives bismuthyl nitrate (BiONO3, also known as bismuth subnitrate or bismuth oxynitrate) when it reacts with water.
Bi(NO3)3 + H2O --> BiONO3 + 2HNO3
Bismuth(III) chloride can be made by reacting bismuth metal with chlorine gas. Alternatively, bismuth metal can be dissolved in concentrated hydrochloric acid if an oxidizer like hydrogen peroxide or oxygen is present. Of course, bismuthyl chloride (BiOCl) is known, but interestingly so is bismuth(II) chloride. I might want to prepare some bismuth iodide from iodine and bismuth once I make some iodine from povidine iodine. Apparently, BiI3 forms dark grey crystals and BiOI exists as brick red crystals. After all, I am a sucker for pretty colors.
A bismuth compound that caught my eye was sodium bismuthate (NaBiO3) in which bismuth is in the +5 oxidation state. This compound allegedly can oxidize acidic solutions of Mn(II) to the beloved permanganate ion! This may provide me with a fairly easy route to potassium permanganate, a chemical I desperately need in my home lab. Sodium bismuthate can be made by oxidizing bismuthyl oxide with bromine or perhaps chlorine.
2BiO(OH) + 6NaOH + 2Br2 --> 2NaBiO3 + 4NaBr + 4H2O
A molten sodium hydroxide melt using air as the oxidant might also work. This is definitely on my never ending list of projects.