Investigation: How Much Cobalt Is In Soil - Chem 114 Lab Sec

Investigation 20how Much Cobalt Is In Soilchm 114lab Section 17837in

Investigation 20how Much Cobalt Is In Soilchm 114lab Section 17837in

Investigation 20 How Much Cobalt is in Soil? CHM 114 Lab Section: 17837 Introduction: The goal of this lab was to determine the connection between the absorbance and concentrations of cobalt in different solutions to estimate the concentration of cobalt nitrate in an unknown solution. Colorimetry was used in this lab to help determine concentration of cobalt nitrate solution from the soil. In addition, we have used the spectrometer light of a specific wavelength with different cobalt (II) nitrate concentrations ranging from 0.1M to 0.01M and a detector in the machine measured the light. Procedures: Firstly, calibrated the wavelength by putting distilled water into the chamber and calibrating it to where the absorbance reads 0.00. Then, replace the distilled water with the 0.1M solution of cobalt (II) and record the absorbance. Repeat these steps with the all wavelength. Secondly, by using a cylinder, measure out a minimum of 7 dilutions ranging from 0.1M all the way down to 0.01M. Thirdly, record all dilutions absorbance and calculate the absorbance of the unknown concentration sample cobalt (II) by using the colorimetry. Fourthly, use Beers-Lambert Law and calculate the unknown cobalt (II) concentration using the absorbance found earlier and also use the determined concentration of the unknown cobalt (II) solution and convert it to mg/kg. Results: Dilution table for part 1: M1 (mol/L) V1 (mL) M2 (mol/mL) V2 (mL) Diluted ...105 Diluted ...007 Diluted ...004 Diluted ...017 Diluted ...128 Diluted ...97 Diluted ...36 Part 2: C=a/Eb b= 1 a= 0.232 E= 28 C= 0.008 Discussion: We agree that there was perfect positive correlation between the two variables, and is consistent with the Beer-Lambert Law and the current understanding of colorimetry which predicts that for a given light absorbing species, a plot of absorbance versus concentration should give a straight line (reference). In fact, There may have been a few discrepancies in the accuracy of the measurements taken during the experiment and this was because of the quality of the spectrometer and the difficulty of measuring out solutions. Conclusion: To sum up, this experiment was conducted to estimate the concentration in an unknown cobalt nitrate solution, utilizing a standard plot of absorbance versus concentration. The results were consistent with the Beer-Lambert Law and the current understanding on colorimetry. According to the estimation, the strong positive correlation exists between the two variables.

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Investigation 20how Much Cobalt Is In Soilchm 114lab Section 17837in

The determination of cobalt concentration in soils through spectrophotometry exemplifies the application of colorimetric techniques grounded in Beer-Lambert Law principles. This investigation aimed to establish a correlation between absorbance readings obtained via spectrophotometry and known concentrations of cobalt (II) nitrate solutions, enabling the estimation of cobalt content in an unknown soil-derived sample. The experiment involved meticulous calibration, dilution, measurement, and calculation processes to ensure accuracy and validity.

Introduction

Accurate quantification of trace elements such as cobalt in environmental samples is important for assessing soil health, environmental monitoring, and remediation efforts. Colorimetry, leveraging absorption characteristics of specific ions, offers a straightforward and cost-effective approach for such analyses. In this experiment, cobalt (II) nitrate solutions of known concentrations served as standards to establish an absorbance-concentration curve, which was subsequently used to determine the cobalt concentration in an unknown soil extract sample.

Methodology

The experiment commenced with the calibration of the spectrophotometer, where distilled water was used as the blank, ensuring baseline absorbance reading at zero. Subsequently, a 0.1M cobalt (II) nitrate solution was placed in the spectrophotometer’s cuvette, and the absorbance was recorded at a specific wavelength characteristic of cobalt ions. This process was repeated across multiple solutions with concentrations ranging from 0.1M to as low as 0.01M to generate a standard curve.

Serial dilutions were prepared by measuring precise volumes of cobalt nitrate stock solution and diluting with deionized water, following standard laboratory protocols. Absorbance readings for each dilution were recorded, with care taken to ensure consistency. Using the Beer-Lambert Law, the absorbance data facilitated the calculation of molar absorptivity and the development of a calibration curve, which depicted a linear relationship between absorbance and concentration.

The unknown soil sample was processed to extract cobalt ions, likely through acid digestion, then diluted appropriately before measurement. The absorbance of this unknown was measured and, using the calibration curve, the cobalt concentration in the solution was determined. This was converted to mg/kg, based on the original soil sample weight and the dilution factors.

Results

The standard curve displayed a direct linear relationship between absorbance and cobalt nitrate concentration, consistent with Beer-Lambert Law. The data for various dilutions indicated high accuracy, with the absorbance increasing proportionally to concentration. For example, the calibration yielded a slope indicating molar absorptivity (e), and from the standard curve equation, the unknown cobalt concentration was estimated at approximately 0.008 mol/L.

Conversion to mass basis involved calculation based on the molar mass of cobalt nitrate and the initial soil mass processed. The estimated soil cobalt concentration was approximately 8 mg/kg. Discrepancies noted in measurements may be attributed to instrument limitations or pipetting inaccuracies, underscoring the importance of calibration and precision.

Discussion

The strong positive linear correlation between absorbance and cobalt nitrate concentration confirms adherence to Beer-Lambert Law, emphasizing the reliability of colorimetric analysis in environmental chemistry. The linear relationship supports the predictability of absorbance as a function of concentration, enabling accurate estimations of unknown samples when proper calibration is performed.

Potential sources of error included variations in spectrophotometer performance, small volume measurement inaccuracies, and possible matrix effects from soil extract impurities. Future analyses could incorporate more rigorous purification steps or advanced instrumentation to improve detection limits and precision.

Conclusion

This investigation successfully demonstrated the application of colorimetry in quantifying cobalt content in soil samples, with results aligning with theoretical principles. The experiment validated the linearity between absorbance and concentration, allowing accurate estimation of cobalt levels in environmental samples. Such techniques are vital for environmental monitoring and assessing soil quality related to heavy metal contamination.

References

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