EXPERIMENT 6 Elemental Analysis By: Abnasan, Stephanie Joy B. Paragas, Regina Monica Noreen C l NH 2 S NH 2 CH 3 O OH OH H HO H OH OH H H CH 2 OH
Oct 15, 2014
EXPERIMENT 6Elemental Analysis
By: Abnasan, Stephanie Joy
B.Paragas, Regina Monica
Noreen
Cl
NH2
S
NH2CH3
OOH
OHH
HO H
OH
OH
H
HCH2OH
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 )
Methodology
Fig 1.1 Setup Apparatus for Sodium Fusion
Test tube holder
5-mL test tube
Burner
Method RationaleA. Sodium Fusion A small piece of sodium was placed in a 5-mL test tube and was heated
using Bunsen burner.In order for sodium to vaporize
The flame was removed and 0.3 grams of the unknown was added.
Test tube was heatedIn order for sodium to react with the
unknown
Method RationaleA. Sodium Fusion
A small piece of sodium was placed in a 5-mL test tube
and was heated using Bunsen
burner.
In order for sodium to vaporize
The flame was removed and 0.3
grams of the unknown was
added.
Test tube was heated
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: -
Test tube was dropped in a beaker containing 10 mL of cold dH20; test tube
is expected to shatter
The liquid molecules expand when placed in an environment of lower temperature.
Because the container can no
longer accommodate the size of the
molecules, causing it to crack. Upon
breakage, excess sodium can react with the unknown
Beaker was placed on a hot plate.
To allow solution to boil; completion of
reactionSolution was filtered. Filtrate was used a fusion solution for
Part B.
Experimental
Theoretical
p-chloroaniline
yellow No change
thioacetamide
Dark violet Dark violet
Glucose White solution
No change
SULFUR TEST: Experimental vs. Theoretical Observation
2. Nitrogen Test
A pinch of FeSO 4 was mixed with 1 mL of
the fusion solution in a test tube
In order for these reactions to occur:
2 NaCN + FeSO4 Fe (CN)2 +
Na2SO4
Fe (CN)2 + 4 NaCN Na4Fe(CN)6
5 drops of 10% solution of KF was
added.
To intensify blue coloration.
The resulting mixture was boiled and then
2 drops of 5% solution of ferric
cyanide was added.
3Na4Fe(CN)6 + 4FeCl3 Fe4[Fe(CN)6]3 + 12 NaCl (blue ppt.)
6M H2SO4 was added. An indication of the presence of nitrogen
is a Prussian blue precipitate
To dissolve the insoluble iron
hydroxides and make the solution acid to
litmus.Thioacteamide: +
Glucose: -p-Choloroaniline: +
The mixture was filtered and the filter
paper was washed with distilled water (if it is impossible to
determine a blue coloration).
to check whether the residue was blue or
not
Experimental
Theoretical
p-chloroaniline
yellow blue
Thioacetamide
blue blue
Glucose White solution
No change
NITROGEN TEST: Experimental vs. Theoretical Observation
3. Halogen Test10 drops of the
fusion solution was placed into a small
test tube.
2 M HNO3 was added
To acidify solution NaX + AgNO3
AgX + NaNO3
The solution was heated to the gentle
boil for about 1 minute and then cooled to room temperature
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.
After which, 4 drops of 0.1 M AgNO3 was
added to the solution. A heavy
curdy-type 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 solubleif Soluble: AgBrnot soluble: AgI
Thioacteamide: +Glucose: -
p-Choloroaniline: +
SampleSufur Test
Nitrogen Test
Halogen Test
Unknown 1 (Glucose)
- - -
Unknown 2 (p-
chloroaniline)
- + +
Unknown 3 (Thioacetami
de)+ + -
Summary of the Qualitative Tests for the Unknowns
Experimental
Theoretical
p-chloroaniline
Heavy curdy ppt.
White ppt. (for
chlorine)thioacetamide
Black ppt. No ppt.
Glucose No ppt. No ppt.
HALOGEN TEST: Experimental vs. Theoretical Observation
1. Outline the procedures for detecting the presence of oxygen
and phosphorus in organic compounds. a. Oxygen
• Ferrox TestSoak 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 100⁰C 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 Schöniger oxidation (also known as the Schöniger Flask Test) is a test in qualitative elemental analysis, developed by Wolfgang Schöniger.
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.
-=Fin =-