Cation Identification Scheme Lab 8

Cations Scheme Lab 8

• This lab outlines a scheme for identifying cations in a solution.
• The scheme involves multiple steps using various reagents to distinguish different cations.
• The scheme identifies cations in five groups (group I-V).
• Cations such as Ag+, Pb2+, Cd2+, Cu2+, Bi3+, Fe3+, Cr3+, Al3+, Zn2+, Mn2+, Co2+, Ni2+, Ba2+, Sr2+, and Ca2+ are examined.

Step I

• Adding hydrochloric acid (HCl) to an unknown solution can precipitate some cations (group I).
• Silver (Ag+) creates a pale yellow precipitate.
• Lead (Pb2+) produces a bright yellow precipitate.
• Further tests confirm these cations with reagents like potassium iodide (KI) and potassium chromate (K₂CrO₄).

Step II

• The solution remaining after Step I is tested for other cations (group II).
• Adding hydrogen sulfide (H₂S) to the solution will precipitate some cations.
• Cadmium (Cd²⁺), copper (Cu²⁺), and bismuth (Bi³⁺) are common examples
• Further tests distinguish between these cations (using ammonia and other reagents).

Step III

• The solution remaining after Step II is tested for further cations (group III).
• Ammonium chloride (NH₄Cl) and concentrated ammonia (NH₄OH) are typically used
• Iron (Fe³⁺), chromium (Cr³⁺), and aluminum(Al³⁺) are common cations.
• Different precipitates are observed when reagents are used.

Step IV

• The solution remaining after Step III is tested for further cations (group IV).
• Adding concentrated ammonia (NH₄OH), ammonium chloride (NH₄Cl) and hydrogen sulfide (H₂S) is typical here.
• The cations being sought include zinc (Zn²⁺), manganese (Mn²⁺), cobalt (Co²⁺), and nickel (Ni²⁺).
• Different colors and precipitates are observed.

Step V

• The solution remaining is tested for cations in the final group (group V).
• This group includes barium (Ba²⁺), strontium (Sr²⁺), and calcium (Ca²⁺).
• Various tests and reagents identify these cations definitively.

General Notes

• Specific colors and types of precipitates are indicators for particular cations in the scheme.
• Confirmation tests are crucial to ensure accurate identification of the cations in solution.
• Steps are designed to isolate and identify cations within specific groups.
• Negative results (no precipitate) are also essential information and sometimes lead to identifying a cation as not being in a particular group.

This lab focuses on a scheme for identifying cations in a solution through various steps and reagents. It details the use of hydrochloric acid and hydrogen sulfide to precipitate different cations and confirms their presence with further tests. Join the quiz to test your understanding of this cation identification process.