The Mystery of Copper Ion Flame Test Colors

[mrjeffy321]

When I stick some Copper (II) Sulfate * Pentahyrate into the blue flame of my butane torch, it turns green.
When I crush the tiny CuSO4 crystals up into a finer powder and mix them with a mixture of KClO3 and Sugar, then light that on fire, I get a very blue flame.
What is happening here? I thought that copper [+2] ions were suppose to color flames blue? How is it that the same substance is giving off two difference colors?

The only exaplanation I could fine for this is,

Copper(II) sulfate decomposes before melting. The common pentahydrate form dehydrates, losing four water molecules at 110 °C and all five at 150 °C. At 650 °C copper(II) sulfate decomposes into copper(II) oxide (CuO), Sulfur dioxide (SO2) and oxygen (O2).

So if this is true, then that would explain it I suppose, assuming CuO produces a blue flame. Except, wouldn't the CuSO4 decompose just as easily in the butane torch flame? If I stick some of the power into the flame and leave it there, watching it, the color should change as it decomposes, but I just don't see that happening.

 

[GCT]

A simple guess would be that you're observing pure copper 2+ ions in the second event while the first may be red-shifted due to solvent effects.

oxides shouldn't be responsible for atomic flame emissions, and the oxides should be forming at the periphery of the flame, You should still observe emissions at, for instance, the interzonal regions of the flame. I don't suppose that any sort of interferences are occurring (spectral and chemical).

I'll have to refer to my I. analysis text, but don't have it with me at the moment.

 

[mrjeffy321]

The a mixture (root killer) of 99% CuSO4 * 5H2O, 1% other inert ingredients.
I do not dissolve it in anything before putting it into the flame. I put the crystals directly into the flame.
Similarly, for the Potassium Chlorate mixture, I crush the crystals into a finer poweder, then just mix it into the KClO3 and Sucrose mix.

Even thought the KClO3 is suppose to burn violet/"lilac", my KClO3 burns much more toward the Yellow-White-Pinkish-Purple side of the spectrum.

 

[chem_tr]

I think you have done a redox reaction. Because chlorate and sugar in the presence of copper(II) ions tend to react with each other. The intensified bluish color may be the result of this redox reaction, along with exothermic nature of the reaction; it might raise the temperature to turn your butane flame more blue, but my assumption is just a brainstorming, not more.

 

[GCT]

nah, don't think that exothermicity is significant in a flame, in fact, at such temperatures, the reverse would probably apply. Supposedly if the atomic emission spectrum of copper II were blue, than a different color would probably relate to a shift in the wavelength of the emitted light; the one's that I can think of are solvent effects (as that when you have copper surrouded with water, fluorescence (stokes shift) although this applies more to molecular emission spectra, or perhaps as you said chemical interference of some sort as if chlorate were to react with copper in an oxidative fashion. I'm pretty new to this also, so I'll need to consider much more sources.

 

[mrjeffy321]

Here is a very recent (within the past 10 minutes + typing time) experiment I did to get some more data, so as to help figure this out.

I took some KClO3 and mixed it with powder CuSO4 * 5 H20, then turned a flame on it. It definitely did not react as violently as it did when I mixed the Copper Sulfate with KClO3 and sugar, but the flame turned blue (the same blue the other Chlorate reaction), with a few small spots of green (the same green from before). There was some reaction going on, no flames or anything and it wouldn't continue on long after I remove the flame, but there was an odor present. The odor was not all that different from that of chlorine gas I think, but it must have been Sulfur Dioxide I figure (why would it form chlorine?).
Then I took some of the KClO3 alone, and put a flame to it. The flame turned yellowish (it should have been violet of course, but this particular batch of chlorate has too many Na impurities).

So it looks pretty reasonable that the Copper Sulfate is reacting with the KClO3 some how, releasing a gas.
Accoring to a lot of info I have seen, copper is suppose to produce a blue flame or (in the case of just metalic copper) a blue-green flame.
http://www.waltnosalek.com/pyro/formulas/List_of_Pyro_Chemicals.htm
So it is working correctly, so to speak, when the chlorate is added to the mix, but by itself its "broken".