ChemLab (stoichiometry) - Molecular Shape and Polarity...

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Molecular Shape and Polarity October 30, 2007 Results and Discussion:
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This experiment’s purpose was to observe emission spectra of various sources with a spectrometer, to create a procedure to determine the composition of a solution containing two or more ionic salts, and to construct a partial energy-level diagram for hydrogen. The spectra produced by each are shown on the attached sheet, and the wavelengths seen are recorded in the following table: Source Fluorescent Light Incandescent Light Helium NaCl LiCl KCl CaCl2 SrCl2 Flame/Gas Color (if applicable) - - orange- white gas orange flame red flame purple -peach flame bright orange flame bright red flame Wavelengths (nm) 550, 435, 615, 580, 490 continuous spectrum 440, 500, 550, 613, 580 589 671 768 553, 588, 624 682, 671, 660, 590 In part B, an unknown mixture (number 4) of two or more of the salts we previously recorded wavelengths for was tested (by putting the unknown on a cotton swab and burning it like the others. The wavelengths observed should be a combination of the wavelengths of the salts already
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Unformatted text preview: observed). This procedure was first tested on a mixture of NaCl and LiCl, producing wavelengths of 589 nm and 671 nm, proving it to be a mixture of NaCl and LiCl. Unknown mixture 4 produced wavelengths of 590 nm, 624 nm, and 555 nm (and an orange flame). Because these values match those of NaCl (589 nm ~ 590 nm) and CaCl2 (624 nm and 555 nm ~ 553 nm), can be assumed that unknown mixture 4 is a mixture of NaCl and CaCl2. The emission spectrum of hydrogen gas (which was purple in color) was observed. The wavelengths included 415 nm, 438 nm, 491 nm, and 661 nm. A partial energy diagram was made as follows on the attached sheet (a sample calculation of the energy follows): E=hcλ E=6.626 x 10-34J*s3.00 x 108 ms-14.15 x 10-7m = -4.79 x 10-19J x 1 kJ x (6.022 x 1 023) 1000 J mol = -288.5 kJ * mol-1 Conclusion: It can be concluded that unknown mixture 4 contained NaCl and CaCl2....
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