Explain the systematic procedures for the ident... - SS3 Chemistry Analytical Chemistry I: Qualitative Analysis Question

The systematic identification of cations in an unknown sample involves a series of tests that are based on the unique chemical properties of each cation. Here is an outline of the procedure for identifying cations:

1.    Preliminary Test: The first step is to perform a preliminary test to determine the pH of the solution. This helps to identify if the sample is acidic, neutral, or basic, which can provide initial clues about the presence of certain cations.

2.    Group Separation: The next step is to perform group separation. Cations are often classified based on their behaviour with specific reagents. The most common groups include Group 1 cations (Ag⁺, Hg₂²⁺, and Pb²⁺), Group 2 cations (Cu²⁺, Cd²⁺, Bi³⁺, Sb³⁺, and As³⁺), Group 3 cations (Al³⁺, Fe³⁺, and Cr³⁺), and Group 4 cations (Zn²⁺, Mn²⁺, Ni²⁺, Co²⁺, and Mg²⁺).

3.    Specific Tests for Cation Groups: Within each group, specific reagents are added to the solution to perform tests and identify the cations present. For example, in Group 1, adding dilute HCl will form a white precipitate with Ag⁺, while no precipitate will be formed with Hg²⁺ and Pb²⁺.

4.    Confirmatory Tests for Individual Cations: After identifying the cation group, confirmatory tests are conducted to identify individual cations. These tests involve reactions specific to each cation. For example, to confirm the presence of Cu²⁺ in Group 2, adding NH₃ (ammonia) will form a deep blue precipitate.

5.    Final Confirmation: To ensure accuracy, further tests may be conducted to confirm the presence of specific cations. These may involve complexometric titrations or specific colourimetric tests.

By following this systematic procedure, chemists can identify the cations present in the unknown sample and establish their concentrations.