21 Jul finishing up a lab report
In this investigation, the county cooperative extension service receives a report that animals appear to be sick from a group of local dairy farmers. The county believes that the animals are suffering from Cobalt deficiency based on the symptoms they are exhibiting. Proper animal diet requires Vitamin B12 in which Cobalt(II) is required for production. The soil for the animals requires .13 to .30 mg of cobalt per kg of soil so that the animals can get the essential vitamins. Soils that are not between the .13 and .30 mg can be altered by adding cobalt nitrate or other compounds made up of cobalt. The county cooperative extension service lacks the proper equipment to conduct an experiment to determine the amount of Cobalt(II) in a solution, so they have contacted the Chemistry 113 Lab class to figure the amount of Cobalt(II) in a solution out. The county cooperative extension service has gone ahead and collected 2.00kg of soil from 20 different farms throughout the county for a total of 40.0kg. After the Cobalt was extracted from the soil, it was dissolved into water, and then concentrated by a factor of 10,000 to prepare 1 L of solution. Because Cobalt ion is a colored species in water, spectroscopic techniques can be used to determine the concentration of Cobalt(II) in an unknown species. Spectroscopic techniques can be used to determine the concentration of Cobalt(II) in an unknown solution, because the cobalt ion is a colored species in water. Percent Transmittance, known as %T, is the relationship between the intensity of the light both before as well as after passing through a solution. Absorbance is A = log(100/%T). In the Beer Lambert Law, A=EbC, the concentration of a light absorbing species is related to the absorbance. E is the molar absorptivity that is specifically for the absorbing species, also known as the proportional constant. The thickness of the light path is known as b and the molarity of the absorbing species is known as C. A Straight-line experience is exhibited in absorbance versus concentration for a given absorbing-light species. By plotting the absorbance versus the concentration of the various solutions of cobalt (II) the concentration of cobalt(II) ion in the unknown example can be determined.
Materials:
· .1M Co(NO3)2(aq)
· Unknown Cobalt Solution
· Graduated Cylinder
· Colorimeter
· Cuvettes
· Tissues
Procedure:
Initially, while wearing PPE, colorimeter was connected to Vernier LabQuest and calibrated to 0 by pouring the water into the cuvette and placing it in the colorimeter. It is important to calibrate between any change in color or concentration to get the most accurate reading. Then taking the 0.1 M solution, create mixed solution with the water by diluting the 0.1 M solution at various levels. Use the formula C(Initial)*V(Initial)= C(Final)*V(Final), where C is the Concentration and V is the Volume, to find what exact initial volume is needed in each solution. For example, to find the volume needed to create a .01M Final concentration in a 5mL volume mutiple .01M and 5mL and then divide that by .1M to find the initial volume of required which would be .5mL of the solution. Afterwards subtract 5 by that number, so 5mL-.5mL to find the amount of water needed in the mixture, which would be 4.5mL in this instance. Once you To Find the Initial Volume, the dilution range for this experiment is .01M to .1M and find the concentration for every .01M between .01M and .1M. Set the colorimeter at wavelength 470nm. Calibrate the machine to 0 between each concentration interval. Record the data and observe the similarities and differences between the patterns of all of the concentration levels.
Data:
Table of the absorbances of dye at different concentrations
| Concentration | Absorbance |
| 0.1 | 0 |
| 0.2 | 0.015 |
| 0.3 | 0.036 |
| 0.4 | 0.042 |
| 0.5 | 0.057 |
| 0.6 | 0.120 |
| 0.7 | 0.130 |
| 0.8 | 0.155 |
| 0.9 | 0.187 |
| 1.0 | 0.20 |
Graph of absorbance vs. concentration
Absorbance at Wavelengths
| 430 nm | 0.145 |
| 470 nm | 0.166 |
| 565 nm | 0.115 |
| 635 nm | 0.005 |
Calculations:
To find initial volume of the cobalt… measure in grams and mL
m(i)V(i)=m(f)V(f)
(0.1)V(i)=(0.02)(5)
= 1, which means we have 1 mL of cobalt and 4 mL of water.
With our data from Table 1, we created a scatter plot with a line of best fit to find the concentration.
The equation is y=mx+b, where y is the absorbance, m is the slope, x is the unknown concentration, and b is given.
.208=2.4012(x)-.0375
x= .102
Then we must use the formula m= (conc.)(V)(MW) to find the mass of the cobalt.
m= (.091)(1)(59.8)
m=6.11g
Then we must convert this number given the fact that this experiment involved 2 kg of soil on 20 farms, then concentrated by a factor of 10,000.
6.11/40/10,000= .016
.13-.016= .144 is the amount of cobalt needed within the soil.
Discussion:
Conclusion:
Works Cited:
1. Bauer, Richard; Birk, James; Sawyer Doug CHM113/116 Lab Manual; Cengage Learning, Boston, MA, 2009
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