Atomic Spectra (Gas Discharge Tubes)

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Page ID: 127572

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Required Training	Required PPE
UC Lab Safety Fundamentals	Lab coat, safety glasses/goggles, nitrile gloves

Equipment	Chemicals
Gas discharge tubes mounted onto a carton box (H, He available)
Hand-held diffraction gratings
Tesla coil
Alligator clips for grounding

Procedure:

1) Ground the system using the alligator clips and cable by connecting one end of the tube to a faucet.

2) Turn on the Tesla coil and gently touch the discharge tube.

3) View the tube through the diffraction grating as a class. You may need to describe what you see to focus the class’s attention to the spectral lines.

4) Collect the diffraction grating.

Discussion:

The diffraction grating must be held as close to the eye as possible to see the spectrum. The room lights should be turned off to make the lines easier to see. The size of the image decreases as the distance from the discharge tube increases.

The Tesla coil is a high voltage energy source. This energy excites electrons in the gas to higher energy states. To return to the ground state, electrons release excess energy in the form of light. The color of the light emitted is dictated by transitions to discrete, quantized energy states.

Using known values of emission spectra, one can perform a similar discharge test on unknown gases to determine which elements are in the unknown gas.

Hazards:

Be absolutely sure the discharge tube is grounded as this demonstration deals with high voltage that may electrocute you.

SOP:

N/A

Disposal (by Storeroom):

Give to the demonstration set-up to the storeroom—no disposal should be required.