Identifying an Unknown Ionic Compound
Chemistry 111-477
Introduction
Through a series of elimination and confirmation experiments, cations and anions are identified by how they react through
different chemical reac
...
Identifying an Unknown Ionic Compound
Chemistry 111-477
Introduction
Through a series of elimination and confirmation experiments, cations and anions are identified by how they react through
different chemical reactions. After doing this, an unknown ionic compound can be classified into its specific cation and anion form by
comparing its characteristics to the ones found earlier.
Materials and Methods
The cation elimination test was performed by having five test tubes, each filled with 10 drops of a cation solution: potassium,
iron (III), zinc, copper (II), and cobalt (II). Then, 6 M NaOH was added drop wise to each test tube until either a precipitate formed or
10 drops were added. To each test tube in which a precipitate formed, 10 additional drops of NaOH were added. The following steps
were then repeated using 15 M NH4OH in place of the NaOH. Each cation was then confirmed with a flame test. (Table 1)
For the anion elimination test, five test tubes were filled with 10 drops each of an anion solution: chloride, sulfite, sulfate,
nitrate, and carbonate. 0.1 M AgNO3 was added drop wise to each test tube until a precipitate formed or 20 drops were added. Each
test tube in which a precipitate formed was centrifuged for five minutes. The supernatants were then decanted and 5 drops of water
was added. Dilute HNO3 was added drop wise to the test tubes until the solution became acidic. The test tubes were then again
centrifuged. The supernatants were decanted and 5 drops of water was added. 6 M HNO3 was then added drop wise until the solution
became acidic. The anion confirmation tests are as followed:
The chloride anion was confirmed by acidifying 10 drops of chloride solution with 6 M HNO3 and then adding 0.1 M
AgNO3. This mixture was centrifuged and the supernatant was removed. 6 M NH4OH was added to the precipitate and then
acidified with 6 M HNO3.
The sulfite anion was acidified with 6 M HCl and then two drops of BaCl2 were added. The test tube was centrifuged and the
supernatant was transferred to a dry test tube. 0.02 M KMnO4 was added drop wise until the color remained. 2 drops of BaCl2
removed the coloration, confirming the anion was sulfite.
The sulfate anion was confirmed by acidifying 10 drops of sulfate solution with 6 M HNO3. 0.1 M BaCl2 was then added
until a precipitate formed.
10 drops of 6 M NaOH was added to the nitrate anion and the solution was then transferred to a dry test tube. A cotton ball
was then placed at the opening of the test tube, along with a piece of red litmus paper while the solution was heated until the
litmus paper turned blue.
The carbonate anion was confirmed by adding 3 drops of 6 M H2SO4 to a 0.2663g sample containing carbonate. A drop of
Ba(OH)2 was then suspended over the mixture. (Table 2)
The identification of our unknown’s cation begu
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