Spectrophotometric Analysis of Mixtures

Spectrophotometric Analysis of Mixtures -...

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Spectrophotometric Analysis of Mixtures: Simultaneous Determination of Cr(III) and Co(II) Solutions GSI: Katie Lutker Kevin Wang Sec 109
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Picture 693 Abstract : The objective of this experiment is to determine the concentrations of Cr(III) and Co(II) within a unknown mixture. These concentrations were determined by the methods of spectrophotometry and the Beer-Lambert Law (A= ε bc ) that describes the relationships between absorbance and concentration. Concentrations of the unknown solutions (as their absorbance is the sum of it components: Cr(III) and Co(II)) were determined by a comparison to the absorbances of the known concentrations. As such, the final results revealed the first unknown solutions to have and and the second unknown solution to have and Introduction : Spectrophotometry is common technique that is utilized to determine a solution’s absorbance of a given wavelength through the use of spectrograph and a photometer. Through the use of a monochormater, white light diffracts through a prism into varying wavelengths of light. It is then that the spectrograph transmits one selected wavelength at a time through the cuvet/solution. Absorbance is measured by the photometer in accordance to the intensity of light. The absorbance of these collective wavelengths is recorded by the spectrophotometer. The Beer-Lambert Law becomes useful as it formulates a relationship between absorbance and concentration of a solutions whereby absorption equals the molar absorptivity, ε (in L/mol-cm), times the path length difference, b (in cm), times the concentration (in M), or A= ε bc. The final determination of this lab produces the component concentrations of Cr(III) and Co(II) within the unknown samples. In order to produce these determinations, two wavelengths with the greatest differences within absorption between Cr(III) and Co(II) must be selected. The molar absortivity of the remaining known and unknown solutions are determined Therefore, using an adaptation of Beer’s law accounting for the two solutions, , we determine the molar concentration of the component ions. Experimental methods : Beginning with .2 (.20002) M and a .05 (.049998) M solutions , a serial dilution was conducted to obtain known concentration of these solutions. The known solutions obtained were: for Cr(III)- a .04 M from .05 M, .03M and .02 M from the .04 M, and .01 M from .02 M of and for Co(II) -a .1 M and .06 M from .2 M, .04 and .02 M from .1 M of . These dilutions were completed using 50 mL volumetric flask and 5, 10, and 25 mL volumetric pipettes. Once the correct concentrations had been obtained, the absorbances of the .03M Cr(III) and .1 M Co(II) were measured within a 1.000cm cuvet with the Spectrum/Peaks mode to determine two wavelengths along the absorbance spectra which yielded the greatest accuracy. The particular
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This note was uploaded on 10/11/2009 for the course CHEM 3 taught by Professor Smith during the Spring '09 term at Aberystwyth University.

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Spectrophotometric Analysis of Mixtures -...

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