Atomic Spectroscopy Lab Report

Introduction: The goal was to analyze light emitted by fluorescent light and atomic sources using spectroscopy. One method was to align the spectroscope’s slit with each light source so only colors emitted from the light source analyzed were present on the scale reading. A second method was to calibrate the spectroscope using fluorescent light’s emission line spectrum. This method was used because the wavelengths of fluorescent light’s emitted colors were known, and scale readings of the emitted colors were determined, making it possible to create a calibration graph. The graph’s equation made it possible to determine the wavelengths of colors from the atomic sources.

Part 1: The wavelengths of emitted colors from fluorescent light’s line spectrum were given. After determining the scale reading of each emitted color from fluorescent light, the spectroscope was calibrated for the atomic sources. The spectroscope was calibrated with fluorescent light because the given wavelengths and the determined scale readings were used to analyze the relationship between wavelength and spectroscopic scale readings. To plot the data, the scale readings from each emitted color of fluorescent light were plotted on the x-axis, while the wavelengths of each were plotted on the y-axis. The data created a graph with a linear trend up and to the right. This represented the trend that as the scale reading increased, wavelength increased. From the data, the equation of the linear trendline, y = 112.31x – 62.501, was found. The R2, or correlation coefficient, was 0.9958. R2 signified the strength of the relationship between two variables. If R2 was positive, the relationship was positive, and vice versa. Fluorescent light’s line spectrum’s R2 indicated a positive relationship between wavelength and scale readings. Fluorescent light’s line spectrum calibrated the spectroscope for the other atomic sources because it created a correlation coefficient and equation that was applicable to the atomic sources.

Part 2: Scale readings of the emitted colors from hydrogen’s line spectrum were measured. Wavelengths of hydrogen’s emitted colors were determined using the equation from the calibration graph (y = 112.31x – 62.501). The change in energy of each emitted color from hydrogen’s line spectrum was calculated using the following equation: ΔE = hc/ƛ. The observed wavelengths of each emitted color were plugged into the denominator. The change in energy values of each emitted color was used to determine the initial energy level of each emitted color. The following equation was used: hc/ƛ = (2.1810-18)*((1/n2initial)(1/n2final)). Once the initial energy level of each emitted color was calculated, the electronic transitions of each were determined. A line spectrum was observed for hydrogen because when hydrogen gas was electrically charged, a hydrogen atom was formed in an excited state, emitting light when it fell to its ground state. Through a slit and prism, light created a line instead of a continuous spectrum because each line was representative of different energy levels the atom could “jump” to. The observed wavelength of blue-violet was 431.67 nm, the accepted wavelength was 434.0 nm, the percent error for it’s observed wavelength relative to its accepted value was 0.5369 %, and it’s electronic transition was n = 5 to n = 2. The observed wavelength of turquoise was 487.81 nm, the accepted wavelength was 486.1 nm, the percent error for it’s observed wavelength relative to its accepted value was 0.3538 %, and it’s electronic transition was n = 4 to n = 2. The observed wavelength of red was 667.51 nm, the accepted wavelength was 656.2 nm, the percent error for itd’s observed wavelength relative to its accepted value was 1.724 %, and it’s electronic transition was n = 3 to n = 2. 

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/bohr.html was used to find accepted values for each emitted color’s wavelength.

Part 3: Nothing was measured for Part 3. The colors of each flame when different Alkali and Alkaline Earth Metals were held in the flame were observed without a spectroscope. The emitted line spectrums of these metals were observed with a spectroscope. A line spectrum was observed for metal atoms because 

when the metal atoms were  electrically charged, the atoms were formed in an excited state, emitting light when each fell to their ground states. The emitted light, through a slit and prism, created a line spectrum instead of a continuous spectrum because each line was representative of the different energy levels the metal atoms could “jump” to.
Sources of Error: One possible source of error was not aligning the spectroscope slit with the light source being analyzed. In Part 1, while the wavelengths of violet, blue, and green were closer to their scale readings (when multiplied by 10-2), the wavelengths of orange and red were 612 and 650 nm and their scale readings were 6.0 and 6.3. The equation from the calibration graph would’ve had a larger slope and a smaller R2 value. The wavelengths calculated for the hydrogen’s emitted colors would’ve been greater than their actual values. The ΔE from the wavelengths and the electronic transitions would’ve been smaller than their actual values. A second possible source of error was not cleaning the nichrome wire before testing each metal atom. If the nichrome wire had remnants of strontium chloride when barium chloride was observed with the spectroscope, it may have caused the “unable to see” observation for barium chloride’s line spectrum.

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