lab 10 revise
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University of Texas, Rio Grande Valley *
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1401
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Astronomy
Date
Apr 3, 2024
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6
Uploaded by AgentMusic2663
Spectra Astronomy 1402 - Online The purpose of this laboratory activity is to examine the atomic spectra given off from excited gases and identify an element by its spectra. Part 1: Background When an atom is excited, electrons change their energy levels to higher ones. When electrons from higher energy levels drop back down to lower energy levels, energy is released in the form of light as shown in the figure 1. The frequency of the emitted light depends directly on the energy between the two orbits and this determines the color of the light. Every element has a unique spectrum of light composed of a set number of different frequencies. If materials are heated, the elemental composition can be determined by resolving those unique spectrums from the emitted light. Figure 1. A photon may be emitted when the electron drops from high energy level to low energy level. White light contains all frequencies of visible light. When white light passes through a prism or a diffraction grating, its component colors are separated and one can distinguish the colors (like in a rainbow). A device specifically designed to separate the components of light and atomic spectra is the spectroscope. A spectroscope contains a narrow slit on one end, a long body, and a diffraction grating at the other end, as shown in Figure 2. When we look at the spectroscope, we see a strong line from the light source in the middle. On both sides of the strong line, we will see relatively weaker spectra. The spectrum is same for both sides but in reverse order. In order to observe the spectrum with your eye, you may look at the spectrum on one side (left or right side). Figure 3 shows an example of a spectrum from a Helium gas spectral tube.
p. 2 Figure 2. Simple diagram of a spectroscope Figure 3. Helium spectrum By observing the spectra of heated materials using the spectroscope, we can identify the chemical compositions of the materials. In fact, this method is commonly used to study the chemical environment of distant stars or planets. In this lab, we study atomic spectra by observing light from gas spectral tubes.
p. 3 Part 2: Activity 1.
Calibrate the Spectra of the Color Plates (page 5). Use a ruler to mark off a linear wavelength scale across the bottom of the color plate such that the experimental wavelengths of the mercury spectrum (bottom Color Plate) correlate with those in the Table 2.1
. Extend the linear wavelength scale perpendicularly and upward across spectra on the color plate, thus creating the same wavelength scale for all of the emission spectra. 2.
Analyze the two spectra of the plate numbers given in Table 3.1
by locating the most intense wavelengths in the given emission spectrum. 3.
Compare the wavelengths of the most intense lines with the data in Table 2.2
. 4.
Identify the element having the shown spectrum, and complete Table 3.1
. Mercury Spectrum Violet 404.7 nm Violet 407.8 nm Blue 435.8 nm Yellow 546.1 nm Orange 577.0 nm Orange 579.1 nm Table 2.1 Record your results in the Lab Report section.
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p. 4 Element Wavelength (nm) Relative Intensity Element Wavelength (nm) Relative Intensity Element Wavelength (nm) Relative Intensity Argon 7 451.1 100 Helium 1 388.9 500 Rubidium 8 420.2 1000 560.7 35 396.5 20 421.6 500 591.2 50 402.6 50 536.3 40 603.2 70 412.1 12 543.2 75 604.3 35 438.8 10 572.4 60 641.6 70 447.1 200 607.1 75 667.8 100 468.6 30 620.6 75 675.2 150 471.3 30 630.0 120 696.5 10000 492.2 20 Sodium 3 466.5 120 703.0 150 501.5 100 466.9 200 706.7 10000 587.5 500 497.9 200 706.9 100 587.6 100 498.3 400 Barium 5 435.0 80 667.8 100 568.2 280 553.5 1000 Neon 2 585.2 500 568.8 560 580.0 100 587.2 100 589.0 80000 582.6 150 588.2 100 589.6 40000 601.9 100 594.5 100 616.1 240 606.3 200 596.5 100 Thallium 9 377.6 12000 611.1 300 597.4 100 436.0 2 648.3 150 597.6 120 535.0 18000 649.9 300 603.0 100 655.0 16 652.7 150 607.4 100 671.4 6 659.5 3000 614.3 100 Zinc 6 468.0 300 665.4 150 616.4 120 472.2 400 Cadmium 4 467.8 200 618.2 250 481.1 400 479.9 300 621.7 150 507.0 15 508.6 1000 626.6 150 518.2 200 610.0 300 633.4 100 577.7 10 643.8 2000 638.3 120 623.8 8 Cesium 5 455.5 1000 640.2 200 636.2 1000 459.3 460 650.7 150 647.9 10 546.6 60 660.0 150 692.8 15 566.4 210 Potassium 10 404.4 18 584.5 300 404.7 17 601.0 640 536.0 14 621.3 1000 578.2 16 635.5 320 580.1 17 658.7 490 580.2 15 672.3 3300 583.2 17 691.1 19 Table 2.2
p. 5 1.
Helium 2.
Neon 3.
Sodium 4.
Cadmium 5.
Cesium/barium 6.
Zinc 7.
Argon 8.
Rubidium 9.
Thallium 10.
Potassium
p. 6 Name Class Date Part 3: Lab Report - Spectra PART II: Identification of the spectra of an element Spectrum # Element 3
sodium 9
thallium Table 3.1
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