Practice Gateway Question

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John Chong
Mrs. Cass
Pre-AP Chemistry
17 September 2012
Practice Gateway Question: Spectral Analysis
Finding the chemical composition of a star is quite a complicated procedure. Stars all give off light and that light comes from the elements that compose that star. Here on Earth, we know which element is which and we can compare their emission lines, when they are excited, to stars’ emission lines. Elements have a ground state and an excited state. Ground state is when the electrons of an atom are in the lowest possible energy state. Excited state is when the electrons of an atom are higher than ground state. We can identify our elements by looking at its emission lines or using a flame test.

One way we can identify elements is through flame tests. When executing a flame test the electrons are excited by the energy of heat from the fire. The test requires one to dip a rod in the substance and put it into the fire. This will excite the electrons of the substance and immediately react by changing the color of the flame. The flame test is described as less accurate than the emission spectra. They both specify which element is which but the flame test’s concluding color must be seen by the human eye while the emission spectra are seen on a spectrometer. A spectrometer is obviously more accurate than the human eye so, the emission spectrum is a more efficient and clear way to identify substances than the flame test.

In Document A, the emission spectrums of the two stars are given. The spectrums of the elements mercury, calcium, sodium, helium, and hydrogen are also given. We can see that some of the elements’ emission lines align with the spectrums of the stars. So in order to find the composition of the stars, we can find the lines of the spectrum of the elements in the stars. The spectra’s elements that fit in the star’s spectra are part of the star. So Star A would be composed of sodium, helium, and hydrogen and Star B would be composed of mercury,...
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