Group IV Cations Analysis
Precipitation of Co2+, Ni2+, Mn2+, Zn2+ using H2S Gas in Alkaline Medium.
1. Setup Experiment
Select Unknown Filtrate
0
1
2
3
2. Observation
Physical State
Clear Solution
Status: Standby.
Assume the filtrate from Group III. In Step 1, excess NH4OH makes it alkaline, and Hydrogen Sulfide (H2S) gas is passed through.
Assume the filtrate from Group III. In Step 1, excess NH4OH makes it alkaline, and Hydrogen Sulfide (H2S) gas is passed through.
3. Chemical Principles
1. Precipitation: H2S is passed in an alkaline medium (NH4OH). The OH- ions combine with H+ from H2S to form water, driving H2S ionization forward. This significantly increases S2- concentration, allowing Group IV sulfides (which have higher Ksp) to precipitate.
• Ni forms a Cherry Red complex with DMG.
• Mn oxidizes to Purple HMnO4 via NaBiO3.
• Co forms Yellow Potassium Cobaltinitrite.
• Zn forms White Zinc Ferrocyanide.
M2+ + S2- → MS↓
2. Specific Tests:• Ni forms a Cherry Red complex with DMG.
• Mn oxidizes to Purple HMnO4 via NaBiO3.
• Co forms Yellow Potassium Cobaltinitrite.
• Zn forms White Zinc Ferrocyanide.
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