"Unlocking the Mystery: How a UV/Vis Spectrophotometer Revealed the Copper Concentration"

When you performed the practical to determine the concentration of Cu²⁺ using a UV/vis spectrophotometer, you obtained an absorbance of 0.6701 for the unknown sample. From the standard curve, you identified that this absorbance corresponds to a Cu²⁺ concentration of 1.78 ppm. ### Analysis and Discussion: 1. **Molar Absorptivity (Slope):** - The slope of the standard curve (molar absorptivity, ε) was 0.1998. This value indicates the absorbance per path length (in cm) and per concentration unit (in ppm) of Cu²⁺ in the solution. - Molar absorptivity is fundamental in Beer's Law (A = εcl), where: - \( A \) is the absorbance, - \( ε \) is the molar absorptivity, - \( c \) is the concentration, - \( l \) is the path length of the cuvette (usually 1 cm). 2. **Correlation Coefficient (R²):** - An R² value of 0.9733 indicates a strong positive linear relationship between absorbance and concentration in the standard curve. - The closer the R² value is to 1, the better the fit of the data to the linear model. A value of 0.9733 suggests that 97.33% of the variation in absorbance can be explained by the variation in Cu²⁺ concentration, indicating a reliable standard curve. 3. **Quality of the Standard Curve:** - The high R² value confirms that the methodology you used to prepare and measure the standard solutions was precise and consistent. - The linearity of the standard curve validates the use of Beer's Law within the concentration range studied. ### Conclusion: The determination of Cu²⁺ concentration using UV/vis spectrophotometry has yielded satisfactory results with an unknown concentration found to be 1.78 ppm. The high correlation coefficient (R² = 0.9733) and a consistent molar absorptivity (0.1998) validate the accuracy and reliability of the measurements and the established standard curve. The data suggests that: - The spectrophotometer and experimental procedure are both reliable for determining Cu²⁺ concentration within the studied range. - The unknown sample, with an absorbance of 0.6701, has been accurately analyzed against the standard curve, providing a concentration of 1.78 ppm. In summary, the experiment was successful, yielding valid and precise results for the concentration of Cu²⁺ in the unknown sample.