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Re: [Phys-l] spectra from flame tests



Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu> writes:
Hello,

I was wondering if anyone has tried to observe the spectra from classic
intro-chem flame tests. I tried this morning, with just a simple
diffraction grating and, for example, some sodium chloride salt (which
glows nicely yellow for the sodium) but was unable to observe any of the
sodium spectral lines at all: the yellow was just one big smudge. I
thought that either 1) I was missing some more careful method to observe
it or 2) that, because of the complexity of the system (sodium, chlorine,
methane in the bunsen burner, oxidation, etc...) that the narrow spectra
lines get washed out in the interactions.

Anyone ever do it, or, know of a more concrete reason it *won't* work?

The flame is too wide to resolve the yellow doublet for sodium. You must
look through a narrow (< .5mm) slit placed between the flame and the
diffraction grating. I have been able to observe very nice spectra with a
fairly inexpensive spectroscope made with a narrow slit and a DG.

PL

Pete Lohstreter "Happy is he who gets to know
The Hockaday School the reasons for things. "
11600 Welch Rd Virgil (70-19 BCE) Roman poet.
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plohstreter@mail.hockaday.org

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