Chemlab: Chemistry 6


Spectrum of the Hydrogen Atom

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Hydrogen Atom Spectrum
With a partner, align the meterstick spectroscope so you can see the visible lines of the Balmer series on meterstick a. Record the value of distance b, once the alignment is optimized. For each visible emission line, record the line position on meterstick a, to the nearest mm, on both sides of the slit. Be sure to record the number of rulings per mm on the grating. The spacing between these equally spaced rulings is the reciprocal of the rulings per mm.

For the second and third parts of the experiment, spectroscopes in your lab group will be set up with different lamps. You and your partner will move from spectroscope to spectroscope to observe the spectra of sodium, helium, neon, mercury, and a fluorescent light.

Sodium Atom Spectrum
Align the meterstick spectroscope to maximize the emission lines visible from the sodium lamp. Record the line positions on meterstick a and distance b, as for the hydrogen spectrum. The yellow line of sodium may appear to be two closely-spaced lines. Record the position of the average of these two lines, and calculate one wavelength.

Fluorescent Lights
Observe the atomic spectra of helium, neon, and mercury at the spectroscopes set up with each of these discharge lamps. Draw an accurate, quantitative sketch of each spectrum, showing the scale on meterstick a and the position of the observed emission lines and their colors. It is not necessary to record a and b values for these spectra, but your sketch should accurately indicate the positions of each line on meterstick a.

Observe the light emitted from the fluorescent light with a meterstick spectroscope. Sketch your observations and describe them in your notebook. The phosphors emitting light in the tube should give a mostly continuous spectrum of visible light, but you should also see brighter emission lines from the gaseous element in the tube. Can you tell which element is present in the tube? You may find that a single element cannot account for all your observations.

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