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Metallic osmium in solid form is nontoxic. But as the compound osmium tetroxide, OsO4, it is extremely toxic, highly corrosive, extremely irritant to mucous membranes. Often considered as one of the most toxic compounds of inorganic chemistry. But then nickel, as tetracarbonyl nickel ( Ni(CO)4 ) could be considered even worse.

No. That "extremely tiny amount of cyanide gas can kill a person" is definitely a myth. Hydrogen cyanide is not extremely toxic. However, under some unfortunate circumstances, the death can be rapid, within minutes.

Highly improbable, although not impossible. Add excess ferrous sulfate, + eventually some ferric nitrate, dilute with plenty of water. Then it will be highly improbable that it will present a hazard of any kind. Of course, reasonable quantities are assuemd, some hundreds of grams at most. It is unlikely to present some hazard, unless the quantity is in orders of tens or hundreds of kilograms.

Nope! The hexacyanoferrate(II)ion is a very stable komplex, which is the reason that it is almost nontoxic (or at least has very low toxicity). On the contrary, one classic way of destructing dangerous alkali cyanide spills is by adding Fe2+ (as solid FeSO4.7H2O). The ferrous ion reacts with the free cyanide ions, giving the very stable complex hexacyanoferrate(II)ion. And this has a very low level of toxicity. Even better; adding some Fe3+ and you get a precipitate of Turnbull blue (=Prussian blue), a complicated phase often described as ~KFeFe(CN)6 (s). But it is possible to convert solid potassium hexacyanoferrate(II) (or hexacyanoferrate(III) ) to KCN by melting it. The potassium hexacyanoferrate is decomposed to nitrogen, ferric carbide, and potassium cyanide. And, boiling a water solution of hexacyanoferrate(II) or hexacyanoferrate(III) with acid gives gaseous hydrogen cyanide. Then you are in a lot of troble!

In what respectis is it "most noble"? Relative what? Sodium is more noble (i.e. less reactive) than lithium with respect to hydrogen, nitrogen, carbon. But sodium is less noble (i.e. more reactive) than lithium with respect to halogens, chalcogens, acids. We see that when reacting sodium and lithium respectively with water. Sodium reacts much more violently, even with ignition, if finely divided or larger chunks. Lithium does not ignite, although the reaction is vigorous.

The term nobility is not uniqely defined from a chemical point of view. Ir is not attacked by aqua regia in any concentration, not even finely divided metal. Au is readily attacked by and dissolved in aqua regia (fast), Pt is dissolved but much slower. But, Au is not oxidized in air at any temp, Ir is attacked even below 1000 deg C, IrO2 is formed. So, which one of these 2 metal is "the most noble"? It is a question of reactivity, and then the reactivity must be specified/defined towards/relative some other species. The electrochemical series is for species (not only metal ions) in water solution. The reason that the redox couple Li+/Li has a lower voltage than Na+/Na, which in turn is lower than K+/K, is solvatization. In water solution that will be hydratization. The result is that by the relative voltages of alkali metal ions i water solution, it looks like Li is the least noble alkali metal, and Cs is the most noble of them. We know from the reactivity of alkali metals towards oxygen and water that it is the opposite situation, at least for the metals exposed to air or moisture. And, the reactivity of alkali metals is not uniqely defined. The reactivity of alkali metals towards halogens, chacogens, acids (and water) increases with increasing atomic number. But, the reactivity of alkali metals towards hydrogen, nitrogen, carbon decreases with increasing atomic number. So Li is the most reactive alkali metal toward nitrogen, not Cs. Li reacts with atmospheric nitrogen at roome temperature and a atmospheric pressure.

Dont even think about it. The melting point for Li is 180,5 deg C, with a serious risk for ignition if the metal is exposed to air. I have once melted Li under (or rather over!) paraffinum oil, and it was just terrible: the oil was very hot, some nasty smoke emanating from the oil, turning somewhat brown-yellow (decomposiing) and the molten metal floating on top of it, totally impossible to get some control over. And with a severe risk of ignition all the time. I guess I was lucky that the bloody metal didn´t ignite right in my face. Don´t handle molten Li, it may ignite right up in your face!

The worst thing I have smelled is POCl3. There was no smell, just an intense burning pain up my nose, my face became violet, black and red. A friend thought I was going to faint. I never did, but the pain was tremendous. The smell was distorted in a strange way, everything smelled like dirty soil. Totally awful. it took about 4 hour before the pain had gone, and the smell was totally recovered.

"Ferrofluid Neodymium Rare Earth Magnetic Liquid - 8 ounces What is Ferrofluid? In short, it is a liquid that responds to magnets and magnetic fields. The longer answer is ferrofluid is an extremely fine powder, coated with a soap-like material called a surfactant, suspended in a mineral oil liquid base. The resulting magnetic suspension is called a ferrofluid. When no magnetic field is present, ferrofluid behaves and flows like a normal liquid. However, when a magnet or magnetic field is introduced, the ferrofluid is attracted to the field. Spikes then form along the magnetic field lines when the magnetic surface force exceeds the stabilizing effects of fluid weight and surface tension. " http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=6193681124&category=413&tc=photo

I am using pure paraffinum oil (thick viscous oil) for alkali metals. This oil is the purest, and with much better preserving properties than ligroin, kerosene etc. For lithium a small polyethylene mesh just above the metal pieces is added. This is to submerge the metal pieces in the oil, well below the surface. Stored in a small thickwalled glas bottle. And this bottle in a metal can, filled with vermiculite. Finally, all alkali metal storage bottles locked in a fire proof safe. By experience I have found that even sodium is preserved unattacked by moisture and oxygen for years under this oil. Potassium is more sensitive, will slowly corrode surfacially. But the real problems are with the 5 reactive lanthanides (La,Ce,Pr,Nd,Eu)! I have found that neodymium is just totally hopeless under paraffinum oil, corrodes heavily. The only method for these metals in the long run is packing under dry argon in sealed glass ampoules.

This one was fun! eating gallium! I haven´t tried that (although I once tasted 1M KCN-solution,; totally awful taste!) It´s correct, Ga is non-toxic by any administration route. Gallium has a very low vapour pressure, and this is in fact used for purifying Ga from more volatile metals like Zn. Zn has a much higher melting point than Ga, but a much lower boiling point. So, by heating Ga (suspended in a radio frequency coil) the Zn gasses of from the melt, but Ga does not. I once saw a listing of vapour pressures for different metals at room temp, and for molten Ga it was something like p(Ga) = 10^-36 atm. That is, no vapour pressure at all at room temp.

By destilling HClO4 you end up with an azeotrope containing ~70% HClO4. Removing water from this is not easy. And highly dangerous. One way of producing water free HClO4 is by treating solid KClO4 with conc H2SO4. Then you get HClO4, no water content. This is not the same as the azeotrope ~70% HClO4. And certainly not the same as chlorine (VII) oxide Cl2O7. It is a completely different fact that Cl2O7 react with water, producing HClO4. "Cl2O7+H2O-->2HClO4. Cl2O7 is perchloric anhydride" Yes, but this does not mean that HClO4 and Cl2O7 is the same thing. SO3 reacts with water, producing H2SO4. But no one would say that sulfur trioxide (sulfuric acid anhydride) is the same thing as sulfuric acid. Or that phosphorus pentoxide is the same thing as phosphoric acid. Etc.

Disproportionation of P4. I have a few sticks of yellow phosphorus under distilled water. After many years undisturbed, I opened the bottle, and was surprised by the weak but very clear smell of rotten fish. Why is this? The bottle is stored in a totally dark room, at somewhat below room temperature. So what happens? Well, P4 reacts rapidly with hydroxide ion in warm water solution, the phosphorus disproportionating to phosphine and hypophosphite ion. But something analoguos actually happens in neutral water solution, very very slowly, and in very tiny amount. However, the amount of phosphine formed is enough to detect a repulsive smell for a short moment when opening the bottle. A bottle of not totally dry commercial red phosphorus also slowly produces a tiny amount of phosphine. Probably this is due to a presence of a small amount of yellow phosphorus contaminating the red variant.

No risk of contaminating the Ga with copper? Probably, it won´t be much anyway.

Commercially available perchloric acid is maximum 73% HClO4. Higher concentration than 85% HClO4 is denoted "anhydrous perchloric acid". "Handling Anhydrous Perchloric Acid (Greater than 85%)": http://www.auburn.edu/administration/safety/crcperchloric.html Chlorine(VII) oxide, Cl2O7, sometimes denoted "perchloric anhydride", is not the same thing as "anhydrous perchloric acid".

Sorrt, my mistake! I mean "chlorine(VII) oxide, Cl2O7, and water free perchloric acid (~100% HClO4)." These are not the same. Storage of Mn2O7? Hmm, it would be dangerous to store that stuff. I wouldn´t try.

I have the same experience with gallium. It will stay liquid until disturbed by some small grain of solid matter that induce crystallization. By some reason, the oxide crust does not induce the crystallization process. But a small speck of dust will. Northern hemisphere: in worst case the temp has fallen down to about -25 degrees centigrade in a really cold winter (south tip of Sweden). In northern region of Sweden (Lappland), I think the most extreme recorded is about -53 degrees centigrade. Well below the freezing point of Hg!

Well - actually, no. Mn2O7 in itself is highly unstable, an may detonate violently upon heating or even a slight mechanical shock! Even without reducing agents present. Comparably unstable compounds are chlorine(VII) oxide, Cl2O7, and anhydrous perchloric acid (~100% HClO4).

Mn2O7 is highly unstable. It is definitely dangerous to produce this anhydride; it decomposes explosively. Often, a tiny amount is produced by putting a single crystal of KMnO4 in conc H2SO4. But no more! There was an accident many years ago in a lab here, where someone made a dangerous mistake. They were going to produce chlorine by mixing solid KMnO4 with aqueous HCl. But someone made a fatal mistake and mixed solid KMnO4 with conc H2SO4. Immediately, a significant amount of Mn2O7 was formed, and exploded violently, completely destroying the fume hood! Avoid this dangerous chemical! As a contrast, the analogous Tc and Re oxides are stable solids. The corresponding anions are not strongly oxidizing anions in contrast to the permanganate ion.

Semiconductor purposes. It turns out that to get a useful semiconductor is much more than just a chemical synthesis of a semiconductor material like gallium phosphide or arsenide. Synthesis of gallium phosphide from the elements is one thing. The production of a working LED is a completely different story! First, purity. The purity of material for semiconductor purposes need to be at least 99,9999% (=6N). This is because even minute amounts of impurities adversely affects the electrical properties of the material. Second, crystal form. The material in semiconductors is not just a solid lump of material, it is a pure single crystal of the material. So you must pull a solid crystal of the material from a melt. And of course, the melt as well as the formed crystal has to be protected from even minute traces of contamination. The vapour pressure of the molten material, as well as the elements, has to be taken into consideration, to prevent some of the materal to evaporise. In this case the vapour pressure of P; Ga has very low vapour pressure even at elevated temp. And then there is the problem of doping the stuff. Then you need some special crystal orientation for the light emission. Etcetera. These are some few of the numerous difficult problems with production of semiconductors. The subject is more that of solid state physics (semiconductor physics) than inorganic chemistry.

A question for jdurg. In your article about phosphorus (chemicalforums) you mentioned that a piece of black phosphorus spontaneously transforms to violet phosphorus, and that nothing can stop this transformation. But black phosphorus is said to be the only stable modification of phosphorus (at room temp and atmospheric pressure). By definition of stability, this should imply that black phosphorus does NOT undergo spontaneous transformation to other modifications. I don´t get it; is black phosphorus stable or not?

I would certainly mind a piece of Po!!! The isotope Po 210 has a half life of 138 days, therefore is incredibly radioactive. But it also has a high vapour pressure (high for metals), slowly sublimes, and heavily contaminates almost any surface in the surrounding. It is incredibly "dirty" and dangerous in this respect. According to webelements: "Weight for weight it is about 2.5 x 10^11 times as toxic as hydrocyanic acid (HCN)." http://www.webelements.com/webelements/elements/text/Po/key.html