Difference between revisions of "Qualitative tests for metals"

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A qualitative metal test is a test to determine the metal ions within a solution or in an alloy.

Methods

Solution tests usually involve color changes or precipitates to categorize what metals are present within a solution. Thus, they are often limited by concentration, and the solubility of a precipitate within a solvent. Since the metals to be tested are in solution, their anions shouldn't matter within a test. In contrast, the tests are usually based upon the fact that certain metals form insoluble salts with certain anions (like sulfates, or chlorides).

Tests

The tests below show methods for the identification of metal cations within solutions. Lists of which metals react in which way may be helpful if added.

• Sulfate test: the sulfate test uses a soluble sulfate (like sodium sulfate), which is added to a solution containing a metal ion. Certain ions will precipitate readily (like barium sulfate or silver sulfate), while others like calcium sulfate may take longer to precipitate. Most transition metals will not precipitate in this test.
• Ferrocyanide tests: Many tests involve the use of potassium hexacyanoferrate(II) and potassium hexacyanoferrate(III), otherwise known as the ferro- and ferricyanide anions. These salts precipitate various transition metals as varied, brightly colored salts. They are also a good indicator of the presence of iron ions, turning a solution deep blue.
• Chlorate/Perchlorate test: Addition of a conc. solution of sodium chlorate/perchlorate to a sample will precipitate any potassium ions present in the sample, due to the low solubility of potassium chlorate/perchlorate.

References

Relevant Sciencemadness threads