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Why is that cations are tested with NaOH and NH4OH?
Accepted Answer
Cations are tested with NaOH and NH4OH to differentiate between different types of cations based on their reactions with these reagents. Here are the specific reactions and observations:
1. NaOH Test:
- Group 1 cations (Li+, Na+, K+): No reaction or formation of a colorless precipitate (if concentrated NaOH is used).
- Group 2 cations (Ca2+, Ba2+, Sr2+): Formation of a white precipitate of the corresponding hydroxide.
- Al3+: Formation of a white, gelatinous precipitate of Al(OH)3, which dissolves in excess NaOH to form [Al(OH)4]-.
- Zn2+: Formation of a white precipitate of Zn(OH)2, which dissolves in excess NaOH to form [Zn(OH)4]2-.
2. NH4OH Test:
- Group 3 cations (Al3+, Cr3+, Fe3+): Formation of a precipitate of the corresponding hydroxide, which is insoluble in excess NH4OH.
- Zn2+: Formation of a white precipitate of Zn(OH)2, which dissolves in excess NH4OH to form [Zn(NH3)4]2+.
These reactions allow for the identification and differentiation of different cations based on their behavior with NaOH and NH4OH.
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