Ashley Schaendorf 4th Hour Atomic Spectra and Atomic Structure Lab Introduction A simple mechanic has an everyday job of fixing problems with peoples cars. They have to determine an unknown. Many people bring their cars to them so that they can figure out what the problem is. They do this by simply running tests and using previous knowledge to determine the “unknown”. Well, this is similar to chemistry. In chemistry wavelengths of emission lines can be determined. A wavelength is the distance between two points, in which a wave repeats. Each wavelength is assigned a certain color, also. Not only are there wavelengths, but there are also line spectrums. These are a pattern of lines that can be seen through a spectrometer, it shows what wavelengths are being emitted. However, by using a spectrometer, there can be a percent error. They can be inaccurate and difficult to read. This is where the percent error comes in. This will show how close the experimental value is to the actual, true value. Therefore, if the wavelengths of emission lines are determined, then the unknowns may be determined. Materials and Methods To begin with, a Bunsen burner and spectroscopes were obtained. The Bunsen burner was lit, and a spray bottle containing calcium was obtained. The calcium was sprayed on the flame numerous times. Observations were taken through the spectroscope and recorded. Next, a spray bottle containing sodium was obtained and the sodium was sprayed on the flame. Observations were taken through the spectroscope and recorded. Barium was next obtained and sprayed on the flame. Observations were taken through the spectroscope and recorded. Lithium was obtained next and sprayed on the flame. Observations were taken through the spectroscope and recorded. Lastly, potassium was obtained and sprayed on the flame. Observations were taken through the spectroscope and recorded. The lab station was then cleaned up and the Bunsen burner was left at the station. The next day, a spectroscope was obtained. The lab was then restarted and completed as a class. Lithium, strontium, potassium, sodium, calcium, barium, and the two unknowns were all placed in that order on top of a lab station. Ethanol was added to the lithium and lit on fire. Observations were viewed through the spectroscope and shouted out and were wrote on the board. Ethanol was added to strontium next and lit on fire. Observations were viewed through the spectroscope and shouted out and were wrote on the board. The same process was completed for potassium, sodium, calcium, barium, and the two unknowns. Lastly, ethanol was lit on fire alone, and observations were viewed through the spectroscope and shouted out and were wrote on the board. The same task was completed using the light bulb that was being used for background light. The observations were copied down. However, the hydrogen portion was not completed correctly and the observations were copied down from another group. The lab was then completed. Ashley Schaendorf 4th Hour Results Table 1: Wavelength Related to Energy Transitions Level 6 to 2 level 5 to 2 level 4 to 2 level 3 to 2 410.76 nm 434.67 nm 486.83 nm 657.22 nm Level 6 to 2 Calculation: 1 / λ = R/H/C(1/(nf)2 – 1/(ni)2) 1 / λ = R/H/C(1/(2) 2 – 1/(6) 2) 1 / λ = 2434500.866 1 / λ = 2434500.866 -1 1 / λ = 4.1076 x 10-7 m x 109 1 / λ = 410.76 nm Observed Wavelength 430 nm 450 nm 500 nm 630 nm Table 2: Hydrogen True Observed Color Wavelength Purple 407 nm Blue 430 nm Teal 485 nm Red 655 nm Observed wavelength 450 nm 510 nm 560 nm 650 nm 710 nm Table 3: Lithium True Observed color wavelength Purple 459 nm Teal 496 nm Light Green N/A Orange 611 nm Red 671 nm Observed wavelength 450 nm 500 nm 570 nm 610 nm 700 nm Table 3: Strontium True Observed color wavelength Purple 405 nm Teal 448 nm Green 502 nm Orange (yellow) 587 nm Red 668 nm % error 5.65% 4.65% 3.09% -3.82% % error -1.96% 2.82% N/A 6.38% 5.81% % error 11.10% 11.60% 13.50% 3.92% 4.79% Ashley Schaendorf 4th Hour Table 4: Potassium Observed wavelength 440 nm 500 nm 560 nm 600 nm 650 nm Observed color Purple Teal Green Orange Red True wavelength 435 nm 497 nm 545 nm (yellow) 590 nm no red Observed wavelength 450 nm 500 nm 560 nm 640 nm Table 5: Sodium True Observed color wavelength Purple (blue) 455 nm Teal 475 nm Green 565 nm Orange 630 nm Observed wavelength 450 nm 510 nm 560 nm 600 nm 610 nm Table 6: Barium True Observed color wavelength Purple 412 nm Teal 490 nm Green 555 nm Yellow 575-585 nm Orange 605-610 nm Observed wavelength 440 nm 500 nm 560 nm 600 nm 650 nm Table 7: Calcium True Observed color wavelength Purple 445 nm Teal 485 nm Green no green Yellow no yellow Orange 615 nm Table 8: Light Observed wavelength 430 nm 450 nm 500 nm 560 nm 610 nm 640 nm Observed color Purple Blue Teal Green Yellow Orange % error 1.15% 0.60% 2.75% 1.69% N/A % error -1.10% 5.26% -0.89% 1.59% % error 9.22% 4.08% 0.90% 2.56% 0.00% % error -1.12% 3.09% N/A N/A 5.69% Ashley Schaendorf 4th Hour Table 9: Ethanol Observed wavelength 450 nm 500 nm 560 nm 640 nm Observed color Purple Teal Green Orange The true wavelengths were either found in the General Chemistry text book or at http://astro.u-strasbg.fr/~koppen/discharge/ Unknowns: Unknown 1 – barium and lithium Unknown 2 – barium and sodium Conclusion At first, this lab was not completed correctly. So, it was then completed as a whole class. Due to this, the lab does not entirely make sense. Many of the students could not read out of the spectrometer, so the readings came from only a couple students. The spectroscopes were also hard to read and somewhat inaccurate. The lighting in the room was inadequate and didn’t light up the spectrum enough to make it readable, unless one was close enough to the flame. The unknowns were determined using the line spectrums and comparing what spectrums were in the unknowns and as well in the other solutions. Looking at the flame would not have been enough, due to the fact that some of the flames looked very similar. All of the solutions were burned in ethanol, also. This could have had an impact on the line spectrum. Many of the line spectrum recordings were the same throughout the lab, such as the 450nm, 500nm, and the 560 nm. This was proven because when ethanol was burned by itself, it had those same exact readings. Possibly, if the lab was completed in individual groups, but each group had enough lighting, the results could have been more accurate. So, as it is visible, figuring out the proper unknown is very important. Not only in chemistry, but it is also important in the everyday world. Teachers often have to figure out an unknown, which is most of the time a no name paper. If the teacher does not find the correct student, the points for the paper could go to somebody else.