|MadSci Network: Chemistry|
There are two considerations when doing flame tests on salts. The first is the temperature of the flame. The second is the type of emissions from the salts.
First, the temperature of the flame must have enough energy to cause emission. A propane/air flame has a temperature of 1925C while acetylene/oxygen flames go up to 3140C. The second part is that with the correct conditions, all elements will have emissions. The reason you don't see them is that the light is not in the visible region of the spectrum. It may be UV or IR. This is how emission spectroscopy works. The machine looks for specific wavelengths of light to measure.
To summarize, there has to be enough energy to excite the element and the light emitted must be in the visible region.
You mention sodium and potassium. Try strontium (red), copper (green), boric acid (green), lead (blue). These are hard to see if sodium or potassium are also present. There is also another test called the borax bead test. This flame test allows you to se Co,Cr,Fe,Mn,and Ni. Ask your instructor for help.
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