EXPERIMENT 6 Elemental AnalysisBy: Abnasan, Stephanie Joy B. Paragas, Regina Monica Noreen
OH H HO H H
O OH H OH OH CH2OH
Elemental Analysis used to determine the presence of atoms in a given sample of organic compound used to determine the structure of a compound and detect the functional groups present used to test for the purity of a given sample
EA can detect the following elements: Carbon Hydrogen Nitrogen Sulfur Oxygen Phosphorus Halogens ( F, Cl, Br, I )
MethodologyFig 1.1 Setup Apparatus for Sodium Fusion
5-mL test tube Test tube holder
MethodA. Sodium Fusion A small piece of sodium was placed in a 5-mL test Method tube and was heated A. Sodium Fusion using of sodium was placed in a 5A small piece Bunsen burner. mL test tube and was heated using Bunsen The flame was removed burner. The flame was removed and 0.3 grams of and 0.3 grams of the the unknown was added. unknown was heated was added. Test tube Test tube was heated
RationaleIn order for sodium to Rationale vaporizeIn order for sodium to vaporize
In order for Sodium to react with the unknown
In order for sodium to react with the unknown
Sodium Fusion Compounds with Nitrogen
Compounds with a Halogen
Compounds with Sulfur
B. Qualitative Tests 1. Sulfur Test 5 drops of the fusion solution and 3 drops of water were placed in a 5mL test tube. 2 drops of 2% aqueous sodium nitroprussside solution was then added. Presence of a deep blue-violet confirms the presence of sulfur.
Thioacteamide: + Glucose: p-Choloroaniline: -
The liquid molecules expand when placed in an environment of lower Test tube was dropped in a temperature. Because the beaker containing 10 mL of container can no longer cold dH20; test tube is accommodate the size of the expected to shatter molecules, causing it to crack. Upon breakage, excess sodium can react with the unknown Beaker was placed on a hot To allow solution to boil; plate. completion of reaction Solution was filtered. Filtrate was used a fusion solution for Part B.
SULFUR TEST: Experimental vs. Theoretical ObservationExperimental p-chloroaniline yellow thioacetamide Dark violet Glucose White solution Theoretical No change Dark violet No change
2. Nitrogen Test A pinch of FeSO4 was mixed with 1 mL of the fusion solution in a test tube 5 drops of 10% solution of KF was added. The resulting mixture was boiled and then 2 drops of 5% solution of ferric cyanide was added. In order for these reactions to occur: 2 NaCN + FeSO4 Fe (CN)2 + Na2SO4 Fe (CN)2 + 4 NaCN Na4Fe(CN)6 To intensify blue coloration. 3Na4Fe(CN)6 + 4FeCl3 Fe4[Fe(CN)6]3 + 12 NaCl (blue ppt.)
To dissolve the insoluble iron 6M H2SO4 was added. An hydroxides and make the indication of the presence of solution acid to litmus. nitrogen is a Prussian blue Thioacteamide: + precipitate Glucose: p-Choloroaniline: + The mixture was filtered and the filter paper was washed to check whether the residue with distilled water (if it is was blue or not impossible to determine a blue coloration).
NITROGEN TEST: Experimental vs. Theoretical ObservationExperimental p-chloroaniline yellow Thioacetamide blue Glucose White solution Theoretical blue blue No change
3. Halogen Test 10 drops of the fusion solution was placed into a small test tube. 2 M HNO3 was added To acidify solution NaX + AgNO3 AgX + NaNO3 to expel HCN or H2S that might be present- if nitrogen and sulfur were present, the compounds AgCN (white) and Ag2S (black) would also precipitate, making it hard to see the presence of silver halide precipitate.
The solution was heated to the gentle boil for about 1 minute and then cooled to room temperature
After which, 4 drops of 0.1 M AgNO3 was added to the solution. A heavy curdytype precipitate indicates the presence of a halogen. A faint turbidity is a negative test. a solubility test was conducted using 0.5 mL of 2M NH4OH and a stirring rod to determine whether the solution is soluble if Soluble: AgBr not soluble: AgI Thioacteamide: + Glucose: p-Choloroaniline: +
Summary of the Qualitative Tests for the UnknownsSufur Test + Nitrogen Halogen Test Test + + + -
Sample Unknown 1 (Glucose) Unknown 2 (pchloroaniline) Unknown 3 (Thioacetamide)
HALOGEN TEST: Experimental vs. Theoretical ObservationExperimental p-chloroaniline Heavy curdy ppt. thioacetamide Black ppt. Glucose No ppt. Theoretical White ppt. (for chlorine) No ppt. No ppt.
1. Outline the procedures for detecting the presence of oxygen and phosphorus in organic compounds.a. Oxygen Ferrox Test Soak filter paper in methanol containing equal amounts of KCNS and ferric chloride
In the presence of oxygen-containing compounds, the complex ion (FeCNS++) distributes itself between the filter paper and the test compound Deep-red colored of solution is observed. Solutions of non-oxygen compounds remain colorless.
Winkler Method Manganese(II) ions liberated from the Manganese Sulfate are loosely bound with excess hydroxide Manganese(II) is oxidized to Manganese(III) in the presence of a strong base and binds the dissolved oxygen Free iodine is produced upon acidification of the sample at a rate of one I2 moleculefor each atom of oxygen. Free iodine complexes with excess iodide ions. The iodine/iodide complex is reduced to iodide with thiosulfate
b. Phosphorus Dip nickel chromium loop into the sample Conduct flame test Using a blue cobalt glass, filter out the yellow sodium Check for the positivity of phosphorous by checking for the presence of a pale bluish green color
Add about 8 drops of HCl to 5 mg of unknown in a 3 mL screw cup vial Close tightly and place it into a 100oC preheated oven overnight Remove the vial from the oven a cool to room temperature Remove the vial cap and place it again into a 100 C oven for an hour to evaporate the acid Add 0.5mL of distilled water to the residue. Then mix it and transfer to a microcentrifuge tube.
After a minute of centrifugation, transfer 5 drops of clear supernatant to a 3 mL vial Add 5 drops of molybdic acid to the solution. Mix the solution and add 2 drops of Fiske-Subarrow reducer Observe for the color changes after 10 minutes. The presence of blue color signifies presence of phosphorus
La Motte Model Fill the test tube to line 6 with the Phosphorus Extracting Solution Use the 0.5 g spoon to add three measures of the sample Cap and shake for 1 minute Remove cap. Allow to stand and sample to settle until liquid above the soil is clear Use a pipet, dropper with the red bulb, to transfer the clear liquid to a second clean test tube
Add six drops of the Phosphorus Indicator Reagent to sample extract in the second Tube Cap and shake to mix the contents Add one phosphorus test tablet Cap and shake vigorously until the tablet is dissolved. A blue color will develop Match the test color with the phosphorus color chart. Record this phosphorus level.
2. Discuss other methods of detecting the presence of sulfur, nitrogen and halogen in organic compounds. Detection of Sulfur In chemistry, the Schniger oxidation (also known as the Schniger Flask Test) is a test in qualitative elemental analysis, developed by Wolfgang Schniger. sample (with C,N,S,H,X) + oxygen (O2) + NaOH Na+X- + Na+NO-2 + Na+2SO-3 (X = Cl, Br, F, I)
Detection of Nitrogen 1. Benzidine Test in the presence of cyanide ions, benzidine is oxidized to give the intensely colored benzidine blue. Oxidation is effected in the presence of cupric ions. The strength of cupric ions as oxidizing agents is greatly reduced in the presence of cuprous ions. Thus, the cuprous ions formed are removed from the test solution. Insoluble cuprous cyanide can be removed by filtration. 2. This test is based on the formation of a red color when the cyanide ion is converted to FeCNS++. (NH4)2SX + NaCN NaCNS + (NH4)2S CNS- + Fe+++ FeCNS++ (red color) 3. Soda Lime Test (Will Varentrop method). Compounds which contain nitrogens liberate ammonia when heated with soda lime. The ammonia liberated is detected with litmus paper or with HCl.
CONCLUSION AND RECOMMENDATIONS The detection of various elements present in an organic compound is called elemental analysis. Carbon and hydrogen are present in almost all the organic compounds. Other commonly present elements in organic compounds are oxygen, nitrogen, halogens, sulfur and sometimes phosphorus. Some of the most common methods included in identifying such are sodium fusion, sulfur test, nitrogen test and halogen test. It was found out that p-chloroaniline turned out to be positive for nitrogen and halogen test (i.e. chlorine); thioacetamide C2H5NS showed positive results for nitrogen and sulfur; and glucose C6H12O6 obtained negative tests for S, N and halogens. For safety measures, students should observe strict precautionary measures. Treat every reagent as toxic that one should never touch it with his/her bare hands. Also, during sodium fusion, one should not allow sodium to be in contact with water as its reaction is highly exothermic. And finally, always do heating procedures inside a hood.