Spectrophotometric Determination of CoCl2 Concentration

Abstract

This study focuses on utilizing spectrophotometry to measure the absorbance of various concentrations of Cobalt (II) Chloride (CoCl2) solutions. By applying the Lambert-Beer Law, we aimed to determine the concentration of an unknown CoCl2 solution. The experiment involved measuring the absorption spectrum of CoCl2 at a concentration of 0.

150 M across different wavelengths to identify the maximum absorbance values. These values facilitated the construction of a calibration curve, enabling the estimation of the unknown sample's concentration. The findings revealed an unknown concentration of 0.050 M at a maximum absorbance wavelength (λmax) of 500 nm, with a calibration constant (k) of 5.4126 and a correlation coefficient (R^2) of 0.9979.

Introduction

Spectrophotometry is a pivotal analytical method in chemistry for quantifying how much light a chemical substance absorbs by measuring the intensity of light as a beam passes through a solution. The principle hinges on the fact that molecules absorb light energy and transition to higher electronic states, with the specific wavelength of light absorbed depending on the molecule's electronic structure.

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This experiment utilized spectrophotometry to dissect the absorbance characteristics of Cobalt (II) Chloride solutions, employing the Lambert-Beer law, which correlates the absorbance of a solution with its concentration and path length. This law is instrumental in creating a linear relationship between absorbance and concentration, enabling the determination of an unknown concentration from its absorbance.

Materials and Methods

Preparation of Solutions

Initial preparations involved creating a series of CoCl2 solutions with varying concentrations by diluting a 0.150 M stock solution with distilled water. The dilutions were carefully measured to produce seven solutions with precise concentrations, outlined in a predefined scheme to cover a broad range of CoCl2 concentrations.

Spectrophotometric Measurement

A calibrated spectrophotometer was used to measure the absorbance of each solution across a wavelength range from 400 to 600 nm. The aim was to identify the λmax for CoCl2, which corresponds to the wavelength at which the solution exhibits maximum absorbance. This data was pivotal for constructing a calibration curve, correlating absorbance values to known concentrations.

Results

Determination of λmax

The spectrophotometric analysis revealed that CoCl2 has a λmax at 500 nm, where it displayed the highest absorbance value of 0.668 AU. This wavelength was consistent across all tested concentrations, indicating a characteristic absorption peak for CoCl2.

Calibration Curve

A calibration curve was constructed using the measured absorbance values at 500 nm for each known concentration of CoCl2. The curve exhibited a strong linear relationship between concentration and absorbance, characterized by a calibration constant (k) of 5.4126 and a high correlation coefficient (R^2) of 0.9979.

Analysis of Unknown Sample

The unknown CoCl2 solution was analyzed using the established calibration curve, yielding an absorbance of 0.272 AU at 500 nm. Applying the Lambert-Beer Law, the concentration of the unknown sample was calculated to be 0.050 M.

Discussion

The experiment successfully demonstrated the utility of spectrophotometry in analyzing the concentration of a solution based on its absorbance. The λmax of 500 nm for CoCl2 was critical for ensuring accurate and consistent measurements across all samples. The calibration curve's high correlation coefficient underscores the reliability of spectrophotometry and the Lambert-Beer Law in quantitative analysis. While the experiment was largely successful, potential sources of error could include instrumental inaccuracies, human error in preparing dilutions, or deviations in the spectrophotometer's calibration. Future experiments could benefit from repeated measurements and cross-validation with alternative analytical methods to enhance accuracy and reliability.

Conclusion

This study affirmed the efficacy of spectrophotometry in determining the concentration of Cobalt (II) Chloride solutions through absorbance measurements. By leveraging the Lambert-Beer Law, we accurately determined the concentration of an unknown CoCl2 solution. The experiment underscored the importance of understanding the molecular and electronic structure in spectrophotometric analysis, providing a robust framework for quantitative analysis in chemistry. The findings highlight the critical role of wavelength selection and the need for precise calibration in achieving accurate analytical results.