Experiment A Spectroscopic determination of Iron with Phenanthroline Unknown # 2 Mass of Mohr’s Salt: 0. 2040 1. 5mL of 6M acetic acid was measured and transferred into a 100mL volumetric flask with a pipette and diluted to the mark. Concentration= [0. 2040(±0. 0001)g/100(±0. 08)mL]*[(1mol/392. 16g)/(1L/1000mL)] = 0. 005202(±0. 09382%) = 0. 005202(±0. 000005)mol/L 2. 10mL of the above stock solution was transferred to a 250 mL volumetric flask and diluted to the mark. Concentration= [0. 005202(±0. 9382%)mol/L]*[10(±0. 02)mL/250(±0. 12mL)] = 0. 00020808(±0. 22607%) = 0. 00020808(±0. 0000005)mol/L 3. Standard error of burette is 0. 02mL in every reading. Solution| Desired Volume| Absorption 1| Absorption 2| Average Absorption| Standard 1| 30| 0. 662| 0. 664| 0. 662| Standard 2| 25| 0. 544| 0. 546| 0. 545| Standard 3| 20| 0. 43| 0. 434| 0. 432| Standard 4| 15| 0. 317| 0. 309| 0. 313| Standard 5| 10| 0. 222| 0. 217| 0. 2195| Standard 6| 5| 0. 113| 0. 112| 0. 1125| Unknown 1| | | | 0. 096| Unknown 2| | | | | 4.
Sample standard concentration calculation with standard 1, Concentration= [30(±0. 02)mL/100(±0. 08)mL]*[0. 00020808(±0. 0000005)mol/L] = 0. 000062424(±0. 2807%) = 0. 000062424(±0. 0000002) 5. From the Calibration curve of Absorbance Vs Concentration, we know the equation of the graph is : y = 10553. 63(±190. 5558)x - 0. 00363(±0. 007721) Where, y is the absorbance and x is the concentration. We know the absorbance of the unknown is 0. 096. Therefore, 0. 096 = 10553. 63(±190. 5558)x - 0. 00363(±0. 007721) x= [0. 096+0. 00363(±0. 07721)]/ [10553. 63(±190. 5558)] = 0. 00000944(±7. 957%) = 0. 0000094(±0. 0000008) 6. Standard Concentrations| Uncertainties| Average Absorbencies| 0. 000062424| 0. 0000002| 0. 662| 0. 00005202| 0. 00000013| 0. 545| 0. 000041616| 0. 000000108| 0. 432| 0. 000031212| 0. 00000007| 0. 313| 0. 000020808| 0. 00000006| 0. 2195| 0. 000010404| 0. 00000005| 0. 1125| SUMMARY OUTPUT| Column1| Regression Statistics| Multiple R| 0. 999348603| R Square| 0. 99869763| Adjusted R Square| 0. 998372037| Standard Error| 0. 008293572| Observations| 6|
ANOVA| Column1| Column2| Column3| Column4| Column5| | df| SS| MS| F| Significance F| Regression| 1| 0. 2109807| 0. 2109807| 3067. 32299| 6. 3634E-07| Residual| 4| 0. 000275133| 6. 8783E-05| | | Total| 5| 0. 211255833| | | | Column1| Coefficients| Standard Error| t Stat| P-value| Lower 95%| Upper 95%| Lower 95. 0%| Upper 95. 0%| Intercept| -0. 003633333| 0. 007720895| -0. 4705845| 0. 66245106| -0. 025069975| 0. 017803308| -0. 025069975| 0. 017803308| X Variable 1| 10553. 63322| 190. 5558304| 55. 3834181| 6. 3634E-07| 10024. 56542| 11082. 0102| 10024. 56542| 11082. 70102| 7. Isobestic point is a specific wavelength at which two chemical species have the same molar absorptivity. A pair of substances can have several isobestic points in their spectra. In a 1-to-1 chemical reaction that involves a pair of substances with an isobestic point, as long as the sum of the concentrations of the two molecular entities in the solution is held constant there will be no change in absorbance at this wavelength as the ratio of the concentrations of the two entities are varied.
This is because the two substances absorb light of that specific wavelength to the same extent. We do not observe any isobestic point in this experiment because we did not scan through the entire spectrum but rather chose a wavelength at which the species have different molar absorptivity. Besides, if we were working with an isobestic point, we would not be able to obtain changes in absorption with changing ratios of concentrations. 8. Transmittance is the ratio of the radiation falling upon a material, to the radiation transmitted through a material.
Absorbance is negative logarithm of transmittance. Molar absorptivity is a measurement of how strongly a chemical species absorbs light at a given wavelength. From Beer’s law we know that, A=? bc. Therefore the absorbance is proportional to the concentration. 9. A solution of Fe34- would show a violet-blue color at an absorbance maximum of 562. And if the absorbance maximum were 414, a green-yellow color would be observed. The spectra for absorbance maximum 562 are sketched in the following: The spectra for absorbance maximum 414 are sketched in the following: 10.
There could be instrument related sources of error. Stray light could be a problem since the detector responds to all the light that reaches it. In liquids, the extinction coefficient usually changes slowly with wavelength, which could add to the possible errors. There could be errors from the measurement uncertainty of the results. There could also be errors while preparations of the standards, due to presence of impurities in the apparatus which may lead to discrepancy in the calculation of the concentration. 11. Van De Water, Leon G. A; Jaap A. Bergwerff, T.
Alexander Nijhuis. UV-Vis Microspectroscopy: Probing the Initial Stages of Supported Metal Oxide Catalyst Preparation. J. Am. Chem Soc. 2005, 127(14), pp 5-24-2025. Academic Search Premier. EBSCO host. University of Minnesota Lib. Twin Cities. Minneapolis. MN. 05/02/12. In this article UV-Vis microscopy is used to monitor macro distribution and speciation of the catalyst precursor species. Through this experiment more detailed information on the structure-function correlation of the catalytic material is obtained. Koeppet, Benjamin; Tolstoy, Peter M; Limbach, Hans-Heinrich.
Reaction Pathways of Proton Transfer in Hydrogen-Bonded Phenol Carboxylate Complexes Explored by Combined UV-Vis and NMR spectroscopy. J. Am. Chem. Soc. 2011, 113(20), pp7897-7908. Academic Search Premier. EBSCO host. University of Minnesota Lib. Twin Cities. Minneapolis. MN. 05/02/12. In this article better insight about the tautomeric states of the H bonded anions, and the solvent configurations were obtained from UV-vis time scale. The UV-vis absorptions were broadened inhomogeneously because of distribution of the H-bond geometries from the different solvents.
