detection of Sulphur and halogens

Apparatus:
Fusion tubes
Test tube
Evaporating dish
Gauze
Tongs
Materials
Sodium metal
Unknown organic compounds A,B,C
0.5M ferrous sulfate
0.5M ferric chloride
3M sulfuric acid
3M acetic acid
3M nitric acid
Sodium nitropusside
Lead acetate
0.1M silver nitrate
Procedure:
Part A: Sodium Fusion Test (Lassaigne)
1. 2-3 drops of unknown substance (for liquid) or 0.1g (for solid) was put into the fusion tube.
2. A piece of sodium was placed into the tube.
3. The tube was hold with a pairs of tong. The heating was gently to avoid spurting out of the sodium. When the sodium was molten, the compound was heated strongly until the end of the tube was red hot (continue heating for 1 minute).
4. The hot tube was plunged into 20ml of distilled water in a evaporating dish and covered with a gauze.
5. The tube was crushed with a pestle.
6. The mixture was filtered into a clean test tube. The colourless and clear filtrate was readily to be examined for the presence of nitrogen, sulphur, and halogens.
Part B: Test for nitrogen (Cyanide test)
1. To 1ml of filtrate, few drops of 0.5M ferrous sulfate was added and a dark green precipitate of iron(II) hydroxide is formed.
2. If sulphur is also present, precipitate will be black. More ferrous sulfate solution was added dropwise to precipitate all the sulphide ion until no more black precipitation is formed.
3. The mixture was heated to boiling with shaking, cooled and acidified with 3M sulfuric acid. If nitrogen is present, a blue colour (Prussian blue) appears immediately on addition of a trace of 0.5M ferric chloride solution.
Part C: Test for sulphur (sulphur test)
1. To 1ml of filtrate, a few drops of dilute solution of sodium nitroprusside were added. If sulphur ion is present, a deep purple colour will appear.
2. Alternatively, sulphide ion may be detected by precipitation as black lead(II) sulphide with lead(II) acetate solution which has been acidified by 3M acetic acid.
3. If halide is also present, white or yellow lead(II) sulphide precipitate may also formed.
Test for halogens
1. 1ml of filtrate was acidified with a few drops of 3M dilute nitric acid.
2. Silver nitrate solution was then added into the solution. Halides are indicated by the formation of a white or yellow precipitate.
Part E
The above procedure was repeated for unknown B and C. For each test, the observations were written down and the elements in the unknown were deduced.
Results:
Table 1 Observations of the unknown compounds on nitrogen test

Unknown compound	Observation on nitrogen test	Inference
A	i) Some dark green precipitate and a little amount of dark precipitate were formed after brownish orange FeSO4 is added. ii) The precipitate become greenish after more FeSO4 is added. iii) The colour of precipitate remained unchanged after heating. iv) The precipitate does not change after sulphuric acid is added. v) Blue precipitate is formed immediately after adding of FeCl3	Nitrogen is present.
B	i) The solution turns to yellow after brownish orange FeSO4 is added. ii) Brownish orange precipitate is formed after heated. iii) Colourless solution is formed after H2SO4 is added. iv) No change after FeCl3 is added.	Nitrogen is absent.
C	i) The solution turns to yellow after brownish orange FeSO4 is added. ii) Brownish orange precipitate is formed after heated. iii) Colourless solution is formed after H2SO4 is added. iv) No change after FeCl3 is added.	Nitrogen is absent.

Table 2 Detection and  Observations of the unknown compounds on sulphur test

Unknown compound	Observation on sulphur test	Inference
A	a) Sodium nitroprusside i) A deep purple solution is formed immediately. b) Acidified lead(II) acetate i) A black precipitate is formed.	Sulphur is present.
B	a) Sodium nitroprusside i) A pale yellow solution is formed. b) Acidified lead(II) acetate i) A white precipitate is formed.	Sulphur is absent.
C	a) Sodium nitroprusside i) A pale yellow solution is formed. b)Acidified lead(II) acetate i) A white precipitate is formed.	Sulphur is absent.

3 detection of halogen Observations of the unknown compounds on halogens test

Unknown compound	Observation on halogens test	Inference
A	Formation of white precipitate after nitric acid and silver nitrate are added.	Halogen is present.
B	Formation of white precipitate after nitric acid and silver nitrate are added.	Halogen is present.
C	Formation of yellow precipitate after nitric acid and silver nitrate are added.	Halogen is present.