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Separation of Inorganics and Organic Compounds from Soil

Essay by   •  January 17, 2012  •  Research Paper  •  4,526 Words (19 Pages)  •  4,043 Views

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b. Explanation of Procedure

Separation of Inorganics and Organic Compounds from Soil

The first step was to effectively separate the organic and inorganic layers. This was accomplished by adding ethyl acetate to 15g of the weighted sample. Ethyl acetate dissolves the organic compounds efficiently without dissolving the inorganic; however, some inorganic was also dissolved as was indicated by the greenish hint of color in the ethyl acetate layer. Thus three extractions with 10mL of distilled water were done to extract out the inorganic compounds. Next, vacuum filtration was done to separate the soil particles from the organic layer. The soil particles were boiled with water. Water was used as an extracting agent because it is very effective at dissolving metal inorganic compounds. Then the solution containing soil was vacuum filtered to isolate the inorganic solution from the sand of the soil.

Inorganic Compounds Detection

The inorganic solution was used to test for the presence of cobalt, nickel or copper, as well as used to obtain the Visible Spectrum to help detect which metals were present. The visible spectrum suggested the presence of cobalt and nickel.

Metal Cation and Anion Tests

Ni2+ Test

To detect for nickel, 15M NH3, and 10 drops of dimethylgloxime reagents were added to the solution. The appearance of a bright red precipitate of the nickel dimethylgloxime confirmed the presence of nickel in the sample. The same was done for standard nickel to confirm the results. UV spec was obtained as a confirmation of nickel in the sample.

Cu2+ Test

To detect copper, 15M NH3 were added to the solution. No deep blue color formed means that there was no copper in the sample just like the visible spectrum had suggested.

Co2+ Test

To detect cobalt, 5 drops of 6M KNO2 were added to five drops of our solution in a clean test tube. The test tube was put in hot water for 15 minutes. The yellow precipitate suggested that cobalt was present in the sample. To confirm that this was the right color for cobalt, standard cobalt was also tested by adding 6M of KNO2 to an equal amount of volume of solution and placed in hot water for 15 minutes. Comparison between the sample's precipitate and the standard's precipitate confirmed the results. Visible spectrum was also obtained for the cobalt to confirm presence of Cobalt in sample.

Anion Test

Since the nickel detection has only one anion, it was an automatic conclusion that it was NiCl2. However for cobalt, there could be two possible anions, Cl- and SO42-. To detect the anion, barium chloride was added to a small amount of the inorganic layer. If chloride was present, then we would not see any precipitate. But if SO42- was present, then precipitate would form because barium sulfate is insoluble in water. There was precipitate in the vial. Consequently, the cobalt in the sample was cobalt sulfate.

Beer's Law Analysis:

Beer's Law analysis is used to find the concentration of the metals using the absorbance of solutions with known concentrations. After deducing the two only possible metal compounds, their concentrations were determined using the colorimeter. The polar portion of the unknown solution was used in this analysis.

Pure metal compounds of cobalt sulfate and nickel chloride were used in the making of the standard solutions. In making the standards, the metal compound that was to have its concentration calculated was obtained and weighed. In addition, the blank solution that was used for this analysis was water for the blanks of both metals. Water was used because the uv spectrum of cobalt sulfate had almost a zero absorbance at 725nm (the maximum absorption wavelength of other metal being tested aka nickel chloride) and vice versa, nickel chloride had its lowest absorbance close to zero at 520nm (the maximum absorption wavelength of cobalt sulfate). This ensured that the absorbance of the nickel chloride in our unknown solution will not have an effect or have minimum effect on the absorbance of cobalt sulfate and vice versa. The primary solutions were made by dissolving the corresponding metal compound in water. After, the solution will be diluted in proportions to create the standard solutions. This is done in a way where the concentration of each standard can be calculated and later plot in a graph. Three standard solutions of different concentrations were made for each metal compounds. Their concentrations were schemed for an appropriate absorbance value to show up using the colorimeter. Appropriate values ranged from 0.10 to 1.00. Each of the standard solutions was run through the colorimeter, using the blank solution (water) as the zero absorbance. The wavelength was set to 510 nm for cobalt sulfate. This was where the peak occurred in its literature UV-vis spectrum. For nickel chloride, the wavelength was set to 725 nm for the same reasons.

The absorbances of the standards were plotted, creating a linear Beer's Law plot which corresponds with the equation A = εlc. After plotting, the slope was taken, which is the molar absorptivity constant ε multiplied with the length of the cuvette tube L (which is 1cm). From this relationship, concentration can be solved for using the known absorbance of the unknown solution.

Initial Identification of Organic Compounds

After obtaining the ethyl acetate from the extraction, TLC tests were done on the organic compounds in order to get an idea of what was present. This was done by spotting our sample against all the other organic standards and seeing which provided the closest match. From this, we were able to suspect the presence of m-nitroaniline. However Borneol was not seen because it evaporated too quickly and its visibly inactive because of lack of pi electrons.

Extraction and Purification of m-nitroaniline

To extract m-nitroaniline, the ethyl acetate layer was extracted with HCl. M-nitroaniline contains an amine group that can be protonated by HCl. The protonation will make m-nitroaniline become water soluble and move to the aqueous layer. Eight

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