Copper Sulfate Determination Using UV-Vis Spectroscopy

In the field of analytical chemistry, precision and accuracy are crucial in determining the concentration of chemical substances. One of the most effective techniques used for this purpose is UV-Visible (UV-Vis) Spectroscopy, a method that relies on the absorption of light by colored solutions. In this experiment, the objective was to determine the concentration of copper sulfate (CuSO₄·5H₂O) solution using UV-Vis spectroscopy and the Beer-Lambert Law.

The experiment began with the preparation of a standard copper sulfate solution. A specific amount of copper sulfate pentahydrate crystals was weighed using an analytical balance. As shown in the photos, approximately 0.6249 g and 2.5050 g of the compound were carefully measured to ensure accuracy. The vibrant blue crystals of CuSO₄·5H₂O are known for their distinct color, which is due to the presence of hydrated Cu²⁺ ions. These ions absorb light strongly in the visible region, making copper sulfate an ideal compound for spectrophotometric analysis.

After weighing, the crystals were dissolved in distilled water to prepare a stock solution. Using a volumetric flask, the solution was diluted to a known volume, ensuring that the concentration was consistent and ready for further dilution. Proper labeling was done on the beaker to indicate the contents and concentration, which is an essential step in any laboratory experiment to maintain organization and avoid contamination.

The next step involved the preparation of standard solutions through serial dilution. This process produced several solutions of decreasing concentration, each displaying a lighter shade of blue. These standards were used to construct a calibration curve, which relates absorbance to concentration. The color change in each dilution visually represented the varying copper ion concentrations.

Using clean 10 mm glass cuvettes, each solution was placed into the UV-Vis spectrophotometer. The instrument was first calibrated to zero absorbance using a blank (distilled water) to ensure accurate readings. As shown in the last image, the absorbance reading began at 0.000 Abs, indicating successful calibration. Each standard solution was then analyzed at the wavelength where maximum absorption (λmax) for CuSO₄ occurs, typically around 800 nm depending on the instrument used.

The Beer-Lambert Law (A = εbc) forms the foundation of this analysis, where A is absorbance, ε is molar absorptivity, b is path length, and c is concentration. The linear relationship between absorbance and concentration allows the creation of a calibration curve, which can then be used to determine the unknown concentration of copper sulfate samples by comparing their absorbance values.

This experiment not only demonstrated the importance of spectroscopic analysis in quantitative chemistry but also emphasized the need for careful sample preparation, precise measurement, and instrument calibration. The vivid blue solutions, the systematic dilution process, and the accurate spectrophotometric readings all highlight how modern chemistry merges visual observation with analytical precision.

Through this experiment, we gained a deeper appreciation for the role of UV-Vis spectroscopy in identifying and quantifying substances. It serves as a powerful tool in various fields such as environmental monitoring, pharmaceuticals, and materials science—proving that even a simple blue solution can reveal complex and meaningful data when examined through the lens of scientific inquiry.

📸 All photos used in this blog were real and personally captured during the actual laboratory experiment. The collage and layout were edited using Canva.

References:
[1] https://chem.libretexts.org/Courses/Los_Medanos_College/Chemistry_6_and_Chemistry_7_Combined_Laboratory_Manual_%28Los_Medanos_College%29/01%3A_Experiments/1.12%3A_Experiment_612_Beer%27s_Law_1_3_4?utm_source=chatgpt.com

[2]
https://webs.anokaramsey.edu/chemistry/Chem1061/Labs/SampleReport/Sample%20Lab%20Report-S13.pdf?utm_source=chatgpt.com

[3]
https://www.mdpi.com/2227-9717/12/7/1408?utm_source=chatgpt.com