Introduction:
A group of farmers has hired our firm to investigate the amount of cobalt (II) that is in their soil. The livestock on these farms have become ill and have been diagnosed with a cobalt deficiency. Soil on these farms should contain between 0.13 to 0.30 mg of cobalt per kilogram. The purpose of this investigation is to determine the amount of cobalt (II) that is present in the soil from these farms in order to determine if a lack of cobalt exists. A spectroscopy technique will be used for this investigation. Spectroscopy is a technique that passes a known electromagnetic radiation wavelength through a substance and measures what remaining wavelengths there were not absorbed by the substance. This will result in the percent of transmittance,%T=II0*100. The transmittance can then be use in the Beer-Lambert Law: A=∈b*C where A is the absorbance, C is the concentration and ∈b is the constant time the thickness of the substance. A graph will then be created with absorbance vs. concentration, where the concentration will be made from a known substance that we will dilute and measure. The result will give a standard curve, which is linear, and the slope of the line will be the value of ∈b. Since we know the concentration we can then determine the absorbance.
Procedure:
Standard lab safety equipment Spectrometer
.1 M Co(NO3)2 (aq) Cuvettes
Unknown cobalt (II) solution Tissues
Volume measuring equipment
To start the experiment the first step was to calibrate the spectrometer with a blank solution, the blank solution used was water, by calibrating the spectrometer will tell what is the best wavelength to use. After the spectrometer was calibrated, the solutions that were used in the experiment were made at different levels of concentration (.1, .08, .06, .04, .02, and 0) by diluting the solutions with water. The solution used in the experiment was Co(NO3)2 cobalt(II) nitrate.After diluting each of the solutions to the appropriate concentration the solutions were placed in the spectrometer to find how much wavelengths were absorbed. After we took a unknown solution, and with the same wavelength used before, the amount of wavelength that was absorbed was found.
Results:
The data to determine the slope of the line:
|
Concentration (M)
|
Absorbance
|
|
0.1
|
0.483
|
|
0.08
|
0.363
|
|
0.06
|
0.276
|
|
0.04
|
0.166
|
|
0.02
|
0.044
|
|
0
|
0
|
The graph with the equation:
λmax=507.6 nm
∈b=4.9743
Cunk=Aunk∈b=0.2824.9743=0.05669
Cunk10000=5.669*10-6M of cobalt
g=M*m=(5.669*10-6)(58.93)=0.000334g
Beer Lambert’s Law is A=εbc
A - absorbance, ε - constant, b - thickness of sample, C - concentration
IL 0.05669mol CO2 x58.93 g/molx 1000 mg/g x1/10000x1/40 Kg=0.000334g CO2/Kg
The amount of cobalt in on kilogram of soil: g Co2+1kgsoil=g2=0.167 mg1kgsoil.
Discussion:
The graph of absorbance vs. concentration, found in the results section, shows the best fit line found between the absorbance, and concentration of the cobalt(II) nitrate found in our soil sample. If R² equals 0.0 then the y value can determined with any given x value. The R² value of the best fit line is 0.276, this value shows a high level uncertainty to predicting the y value from the value of x. It’s clear that the best fit line, formed by the formula y = 5.114(x) + 0.056 to solve for the linear equation of absorbance vs. concentration differs and that leaves us with an R² of 0.276. The found concentration of cobalt(II) nitrate per kilogram of soil was found to be approximately 0.000334mg, which is below the lowest concentration required; 0.13mg per kilogram of soil. An additional 0.1296mg of cobalt(II) nitrate needs to be added to each kilogram of soil to meet the minimum concentration required, to provide the nutritional needs of the animals.
Conclusion:
In conclusion we were able to determine that the amount of cobalt in the soil was within the standard amount needed for proper animal diet, but should consider giving soil a minor addition of cobalt nitrate. The determined value is really close to the minimum amount for proper animal diet. We would also recommend looking at other variables that could cause the illness of the livestock. This investigation was a success in determining the amount of cobalt in the farmer's soil. The spectroscopy technique and the Beer-Lambert’s Law was a great utilization for this investigation because everything could be measured with control of the tests and the cobalt ion in water has a reddish color to it and could be used.