DFliyerz
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Colored Alkali/Alkaline Earth Metal Salts?
I know that most if not all of the salts of alkali and alkali earth metals are white or colorless, but are there any that have colors like transition
metal salts, maybe even corresponding to their flame colors?
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j_sum1
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The only one I am aware of is the lovely purple copper complex easily made as a precipitate of copper sulfate and sodium dichlorocyanuric acid. I
hardly think that qualifies as a group 1 salt however. For what it's worth, I have made a small amount of an analogue using potassium in place of the
sodium.
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Molecular Manipulations
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The group I and II ions are always colorless. Since most common anions are also colorless (eg. chloride, sulfate, nitrate), most of the common salts
they form likewise have no color.
There's many transition metal polyatomic anions who's group I or II salts are colored. This color comes solely from the transition metal. Some
examples of these are chromates, permanganates and cuprates. Nearly all transition metals can form these, so there's acually hundreds of colored
compounds like this.
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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nezza
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I thought that some of the trihalides of the higher atomic number elements such as CsCl3 are coloured yellow or orange.
If you're not part of the solution, you're part of the precipitate.
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Amos
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If you count something like sodium dichromate, which is bright orange and gives a yellow-orange flame color characteristic of sodium, then yes, there
are some. But let's be honest, the color isn't really dependent on the alkali metal at all.
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DraconicAcid
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The anion may be coloured, but the alkali metal has nothing to do with it. The colour depends on absorption of photons in the visible region, which
requires either a partially filled d subshell (not present in alkali metal cations), conjugated pi bonds (not present in alkali metals), or the
possibility of internal redox reactions (not present in most alkali metal compounds). The closest thing you can get to a coloured alkali metal
compound without using a coloured anion would be the blue solutions of alkali metals in liquid ammonia, or sodium chloride that has been exposed to
enough UV radiation to get rid of some of its chlorine, so that it has an excess of sodium (http://en.wikipedia.org/wiki/F-Center ).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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blogfast25
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Quote: Originally posted by nezza  | | I thought that some of the trihalides of the higher atomic number elements such as CsCl3 are coloured yellow or orange. |
Did you mean various unusual Cs oxides?
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Texium
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I believe woelen did some work with cesium trihalides, such as
cesium tribromide, which is bright yellow-orange, although I can't find the page now. I did however find another one of his experiments making a yellow potassium polyhalide.
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woelen
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Alkali salts of colored anions are not interesting in this context. So, the copper salt, mentioned above, and the dichromates and polyhalides all can
be dismissed as colored salts of the alkali metals. They simply are colored because of the anion.
There are, however, some salts, which are truly colored, because of the use of the cesium ion. I recently made one.
The ions SbCl6(3-) and SbCl6(-) are colorless. Alkali salts of these ions exist and these salts are white. However, when the rubidium or cesium salts
are made of a mix of SbCl6(3-) and SbCl6(-), then a very dark blue/violet color is obtained. This is specific for cesium and rubidium. With potassium
or lower alkali ions, the salt simply behaves like a white mix of SbCl6(3-) and SbCl6(-), but the larger Cs(+) and Rb(+) ions apparently cause the
crystal lattice to become such that there is a special interaction between the cations, leading to strong colors.
Another interesting example of a colored cesium salt is Cs2O. Other oxides (not peroxides and superoxides) of alkali metals are white. I myself have
Na2O and this is a totally white powder, which dissolves in water with production of a lot of heat. Cs2O, however, is yellow/orange. In this case,
there is interaction between the metal ion and the oxide ion, which makes it appear orange. Solutions of Cs2O in water (which are solutions of CsOH
after reaction), however, are colorless.
Other oxides of Cs are strongly colored as well. Cs3O, Cs4O and even lower oxides of Cs seem to exist, which have very strong colors. Cs2O2 is yellow,
like Na2O2. CsO2 is yellow/orange, like KO2.
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