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Organic Chemistry 1 Year Laboratory Report Experiment No: 1 Title of Exp
: Qualitative Elemental Analysis
Date of Exp
: 19 November 2013
Name
:Linda Aida bt Mohd Zaid (SED120005)
Group
:O
Subject
: Organic Chemistry 1 Year
Lecturer
: Dr. Thorsten Heidelberg
Tutor
: Miss Liew Sook Yee
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Experiment 1
Title: Qualitative Elemental Analysis.
Objective: To analysis and identify elements that are present in the unknown sample by
using sodium fusion test, followed by qualitative analysis for ions produced by the fusion.
Introduction: Qualitative analysis of organic compound helps identify and characterize
unkown organic compounds . The analysis and identification of the structure of unknown substances constitutes a very important part of experimental organic chemistry .The determination what elements are presents in the sample is the common first step in the identification of an unknown substances. The used of spectroscopic techniques by organic chemists to establish the structure of a compound. However, it is often useful to supplement the spectral data with other information such as the existence of elements other than carbon, hydrogen and oxygen straight forward chemical test was used to determine elements in organic compound such as nitrogen , sulphur , iodine, chlorine and bromine . The Lassaigne’s test or known as sodium fusion test was developed by J.L Lassaigne which is method used for the quantitave determination. Sodium is a very strong reducing agent that will able to breal up the organic compound atom chain , The organic compound is fused with metall ic sodium to convert these elements into ionic mixture which dissolved in water and the filtrate was used to perform the test . The organic substances was heated with sodium metal under condition tha ensure the conversion of nitrogen sulphur and halide into inorganic substance as shown below.
Organic compounds + Na 0
NaCN + Na2S + NaX + NaOH
(Containing C, H, O, N, S, X)
( X= Cl, Br or I)
Apparatus: Pyrex test tube (4.5 X 45 mm), test tube, evaporating dish, tongs, glass rod, wire
gauze, filter paper
Chemicals: Sodium metal, unknown C compound, distilled water, dilute sulphuric acid,
dilute acetic acid, 1% lead acetate, 5% silver nitrate, dicloromethane, 5% sodium hypochlorite, 5% nitric acid, 0.1M silver nitrate, 0.1% NaOH
Procedure :
Lassaigne’s Test.
1. 10mg or 10μL of the C unknown and 50mg freshly cut sodium metal are placed into a glass tube. Avoid all contacts with water when handling sodium. 2. The glass tube is heated strongly until the bottom of the tube is glowing red and the tube is hold for 2 minute. 3. Then, the hot tube is immersed quickly in evaporating dish containing 10ml of distilled water and covered the dish with wire gauze to avoid any splatter. 4. Next, the solution is boiled for a few minutes while the residue is crushed gently with a glass rod. 5. The colorless solution is filtrated using a filter paper into a test tube for the various test below. 6. The fusion should be repeated if a colored filtrate appears as it indicates incomplete deposition.
Test for nitrogen
1. 2ml of the filtered fusion solution was added to a tube containing 0.14g powdered iron (II) sulphate crystals. 2. The mixture was heated with shaking . Without cooling, a sufficient dilute sulphuric acid is added to dissolve the gelatinous hydroxides of iron of the mixture. 3. A Prussian blue precipitate of iron (III) ferrocyanide Fe [Fe (CN) 6]3 was appeared indicate that nitrogen is present. 4. If the blue precipitate does not appear immediately, the mixture is allowed to stand for 15 minutes. Then the mixture is refiltered through a filter paper and the paper is washed with water to remove all coloured solution. 5. Prussian blue present should be visible on the paper. If there is doubt whether Prussian blue formed or not, another sodium fusion test should be carried out and the test to be repeated. 6. The solution should be pale yellow in colour if there is absence of nitrogen due to iron salts. 7. Black precipitates of iron (II) sulphide appear if sulphide ion is present. The mixture is boiled for about 30 seconds and the mixture is acidified with dilute sulphuric acid.
8. The iron (II) sulphide will dissolve and a precipitate of Prussian blue will appear if nitrogen is present.
Test for sulphur
1.
Diluted acetic acid was added to acidified 2 ml fusion solution .
2. A few drops of 1% lead acetate were added into the solution. 3. A black precipitate of lead sulphide appears indicates the present of sulphur in the solution.
Test for halogens Nitrogen and/or sulphur present
1. 1 ml of the fusion solution is acidified with dilute acid and concentrated to half of its volume to remove any hydrogen cyanide or h ydrogen sulphide present in the mixture. 2. The reactions are carried out in a fume cupboard. 3. The mixture is then diluted with an equal volume of distilled water. 4. 1-2 drops of 5% of aqueous silver nitrate is added to 2-3 ml fusion solution. 5. Heavy precipitation indicates the presence of chlorine, bromine or iodine.
Nitrogen and sulphur absent
1. Dilute nitric acid is used to acidify fusion solution and excess of 5% silver nitrate is added to the solution. 2. Precipitate indicates the presence of chloride, bromide and iodide. Silver chloride is white, silver bromide is pale yellow and silver iodide is yellow. 3. Each has different solubility in 5% ammonium hydroxide solution. 4. The solvent is decanted and the precipitate is treated with dilute aqueous ammonia solution and 2ml of 5% ammonium hydroxide. 5. Silver chloride is soluble in ammonium hydroxide, silver bromide is slightly soluble and silver iodide is insoluble in ammonium hydroxide.
Test for iodine
1. 3ml of fusion solution is acidified with 10% sulphuric acid solution and the fusion solution is boiled for a few minutes. 2. 1ml of dichloromethane is added after cooling followed by a drop of 5% sodium hypochlorite (bleach). 3. Purple or violet colour produced in the dichloromethane layer indicates the presence of iodine.
Test for bromine
1. 3ml of fusion solution was acidified with 10% sulphuric acid solution and the fusion solution is boiled for a few minutes. 2. 1ml of dichloromethane is added after cooling followed drop by drop of 5% sodium hypochlorite (bleach) while shaking it until the purple colour disappeared. 3. Appearance of reddish brown colour indicates the presence of bromine.
Test for clorine
1. The filtrate was acidified with 5% nitric acid and the solution is boiled for a few minutes. 2. A sufficient amount of 0.1M silver nitrate is added to precipitate out the halogen completely as silver halides. 3. Then, the precipitate was filtered and added 3ml of 0.1% NaOH solution. 4. The mixture is boiled for about 2 minute and the solution is filtered. 5. The filtrate is next acidified with 5% nitric acid and added a few drops of 0.1M silver nitrate. 6. A white precipitate indicates the presence of chlorine.
Results :
Tests for the presentation of elements
Observation and results
Nitrogen
Prussian blue precipitate formed
Sulphur
No black precipitate formed
Nitrogen and/or sulphur present
Heavy white precipitate formed
Iodine
No purple or violet colour in the dichloromethane formed
Bromine
No reddish-brown colour formed
Chlorine
White precipitate formed
Discussions:
Lassaigne’s test was used to detect the presence of elements .I used sodium because sodium is a very strong reducing agent. So , its can be used to reduce those atoms that are covalently bonded to the carbon chain to inorganic soluble ions.Test for nitrogen in the compound C shown a Prussian blue precipitate of iron(III) ferrocyanide appears . the nitrogen can be reduced to form cyanide ions, CN- . When the heated of the mixture of fusion solution and powdered iron (II) sulphate crystals were added with diluted sulphuric acid, a Prussian blue precipitate of iron(III) ferrocyanide appears. For the test sulphur , I used a few drops of 1% lead acetate and dilute acetic acid are added to the fusion solution but there is no black precipitate of lead sulphide formed. That show compound C did not have sulphur on their structure . This compound C have nitrogen but sulphur absent . So the cyanide ions have remove by acidify 1 ml of the fusion solution with dilute nitric acid and concentrate to half of its original volume .This can expel any hydrogen cyanide that presents in this compound C .Then the filtrate the compound C was mixed with 2 drops of 5% of aqueous silver nitrate solution .Its produce the result immediate heavy precipitation indicates the presence of halogens .
For halogen test , I got negative result for iodine and bromine which shown compound C have non of this mixture . While for chlorine test I got positive result which shown a white precipitate. The precaution step should be taken wearing safety glasses . I not used to wear safety glasses so I have to make sure worn it in the laboratory at all the time . Next used a small flame when heat the tube . To make sure our skin especially hand get contact with corrosive sulfuric, nitric and acetic acids have to wear gloves .
Answer for question:-
1. Na2S
+
Pb(C2H3O2)2
→
PbS
+
Na2(C2H302)2
(black precipitate)
2. The mixture is boiled in a fume cupboard to expel nitrogen and sulphur because cyanide gas and sulphide gas is very poisonous and the toxicity in air can prevents cellular respiration. At high concentration, cyanide gas is explosive.
3. The sodium wastes are destroyed in the waste bottle which located in a fume cupboard .
Conclusions:
From the conducted tests for the unknown C compound, I conclude that the C compound consists of nitrogen and chlorine.
