Honors Chemistry (820), 2017-18
Thursday, October 25, 2007 10:46 AM
In this experiment you will observe light from various sources and learn how to distinguish between a continuous spectrum and a line spectrum.
In 1853, the scientist Anders Angstrom passed a current through a sealed tube filled with hydrogen gas. When he viewed the resulting light through a prism he saw a line spectrum. This was one of the first clues that the atom possessed an internal structure. Later on, Bohr devised a model of the atom that explained the line spectrum of hydrogen. In this experiment, you will view the line spectrum of hydrogen and other elements using a spectroscope. Each element has its own characteristic pattern of spectral lines. The uniqueness of each element’s line spectrum serves as an “atomic fingerprint” that identifies an element.
A spectroscope is an instrument that separates light by diffraction according to its wavelength. The light enters a narrow slit and hits a diffraction grating, where it is separated into the colors it contains. When you look through the spectroscope you see the different colors of light displayed. The spectroscope has a scale on it that allows you to measure the wavelength in nanometers (1 nm = 10–9 m). A continuous spectrum has all wavelengths of light. When viewed through a spectroscope, a continuous spectrum looks like a smooth rainbow of colors. In contrast, a line spectrum only has certain wavelengths of light. When viewed through a spectroscope a line spectrum looks like a set of distinct colored lines.
Be certain that you can identify the equipment and reagents listed below, before starting the experiment.
The gas discharge tubes (gas filled bulbs) get very hot. Be careful not to touch hot discharge tubes.
Go to each station and use a spectroscope to view the light from the light sources. Record your observations on the data sheet. Use the colored pencils to indicate the colors that you see.
Answer the following pre-activity questions. Record your answers in your laboratory notebook, or on the available report form according to the instructions from your teacher
Record measurements for each day as indicated either in your laboratory notebook, or on the report form provided per the instructions of your teacher.
Answer the following questions either in your laboratory notebook or on the post-activity question sheet supplied according to the instructions from your teacher.
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