Determination of Chromium (Vi) by Direct Visible Spectrophotometry (External Calibration Method)
Experiment No. 3
Determination of Chromium (VI) by Direct Visible Spectrophotometry
(External Calibration Method)
Group Members: Cabahug, Elisha Niña M. Date Performed: November 20 & 22, 2012 Mejia, Helen Mae N. Date Submitted: November 29, 2012
Score:
I. Introduction
Spectrophotometric measurements with UV or visible light radiation are useful in detecting transition metal ions and highly conjugated organic compounds. In UV and visible light regions, energy spaces molecules undergo electronic transitions. By comparing the spectrum of an analyte with those of sample molecules, you can get an idea as to the identity of the absorbing groups.
Solutions of transition metal ions can be colored (i.e., absorb visible light) because d electrons within the metal atoms can be excited from one electronic state to another. The color of metal ion solutions is strongly affected by the presence of other species, such as certain anions or ligands, an example of this is the chromium (VI), Cr (VI) specie. The Cr (VI) present in potassium dichromate will be determined using direct visible spectrophotometry.
The calibration process is employed in this experiment since it is essential in every analytical procedure. The external calibration method will be done in the experiment.
II. Objectives
a. To determine the wavelength with maximum absorbance of chromium (VI) specie. b. To calculate the molar absorptivity of the different concentrations of potassium dichromate by applying the Beer’s Law. c. To apply the external calibration method in determing an unknown concentration of potassium dichromate solution.
III. Procedure
NOTE: Remember to set the OA or 100% T every time the wavelength setting is changed using the blank solution. Also take the absorbance reading of your solution 10 nm increments within the 50 or 100 nm ranges where the absorbance is at maximum. IV. Results and Discussion
Chromium (VI) is highly
Determination of Chromium (VI) by Direct Visible Spectrophotometry
(External Calibration Method)
Group Members: Cabahug, Elisha Niña M. Date Performed: November 20 & 22, 2012 Mejia, Helen Mae N. Date Submitted: November 29, 2012
Score:
I. Introduction
Spectrophotometric measurements with UV or visible light radiation are useful in detecting transition metal ions and highly conjugated organic compounds. In UV and visible light regions, energy spaces molecules undergo electronic transitions. By comparing the spectrum of an analyte with those of sample molecules, you can get an idea as to the identity of the absorbing groups.
Solutions of transition metal ions can be colored (i.e., absorb visible light) because d electrons within the metal atoms can be excited from one electronic state to another. The color of metal ion solutions is strongly affected by the presence of other species, such as certain anions or ligands, an example of this is the chromium (VI), Cr (VI) specie. The Cr (VI) present in potassium dichromate will be determined using direct visible spectrophotometry.
The calibration process is employed in this experiment since it is essential in every analytical procedure. The external calibration method will be done in the experiment.
II. Objectives
a. To determine the wavelength with maximum absorbance of chromium (VI) specie. b. To calculate the molar absorptivity of the different concentrations of potassium dichromate by applying the Beer’s Law. c. To apply the external calibration method in determing an unknown concentration of potassium dichromate solution.
III. Procedure
NOTE: Remember to set the OA or 100% T every time the wavelength setting is changed using the blank solution. Also take the absorbance reading of your solution 10 nm increments within the 50 or 100 nm ranges where the absorbance is at maximum. IV. Results and Discussion
Chromium (VI) is highly
References: * Skoog, D. A., F. J. Holler and S. R. Crouch. 2007. Principles of instrumental analysis 6th ed. Thomson Brooks/Cole. Canada. * Skoog, D. A., D. M. West, F. J. Holler and S. R. Crouch. 2008. Fundamentals of analytical chemistry 8th ed.. Thomson Brooks/Cole. Singapore * Chirium Laboratory site.htm * Bobby Stanton,Lin Zhu,Bobby Stanton, Lin Zhu, Charles "Butch" Atwood,Charles H. Atwood. Experiments in General Chemistry: Featuring MeasureNet.