Activity 14: Lassaigne's Test Flashcards
A qualitative elemental analysis or test carried out to detect the presence of N, S, and Halogen ( Cl, Br, I) and oxygen in an organic compound.
Lassaigne’s test
The first step in lassigne’s test is the treatment of a small sample of the compound with ________________, a powerful reducing agent, to convert all N, S and halogen to cyanide, sulfide and halide respectively.
molten sodium metal
The presence of sulfide is detected by __________________
the addition of lead acetate to acidified solution of the fusion mixture.
If Sulfur is present, there is a formation of __________ precipitate or the __________
black
lead sulfide
The presence of cyanide is detected by _________
the filtered basic solution is treated w/ aqueous ferrous sulfate and ferric chloride, boiled for a few minutes and acidified w/ sulfuric acid.
If cyanide is present, there is a formation of a _____________ precipitate or the __________
prussian blue
ferric ferrocyanide
The presence of halide is detected by ________
precipitating it as a silver halide by the addition of silver nitrate to the acidified test solution.
In halides, if the precipitate is soluble, __________ is present ; if insoluble, _______________ is present; if partially soluble, _____________.
(a) Chloride
(b) Iodine
(c) Bromine
In halides, if there is a formation of precipitate:
(a) if the precipitate is white and soluble it is ___________
(b) if the precipitate is yellow and insoluble, it is ______________
(c) if the precipitate is pale yellow and partially soluble, it is _________________
(a) AgCl
(b) AgI
(c) AgBr
Why is it necessary to react the test compound with fused sodium metal before any elemental analysis is done?
to convert all nitrogen, sulfur, and halogen into inorganic form (cyanide, sulfide and halide) so that they will respond to the inorganic reagents.
Expalin how these interferences are avoided in the following tests:
FeS in test for Nitrogen
adding ferrous sulfate and make alkaline by adding enough NaOH solution then boil and filter to remove FeS
Expalin how these interferences are avoided in the following tests:
Ag2S and AgCN in test for halogen
acidify w/ HNO3 then boil the solution to expel HCN and H2S
Indicator that the sodium fusion part is complete and the fusion tube can now be dropped into the beaker with water
A red hot tube
In the test for presence of halogen, what will happen if S or N is present and the solution is immediately added w/ AgNO3 without boiling
Ag2S and AgCN will form and interfere with the result
