Overview
The lecture covers the identification and separation of Silver Group (Group 1) cations—silver, lead, and mercurous ions—through precipitation and confirmatory tests to detect impurities in pharmaceutical inorganic analysis.
Introduction to Silver Group Cations
- Silver Group (Group 1) cations include silver (Ag⁺), lead (Pb²⁺), and mercurous (Hg₂²⁺) ions.
- These cations must be separated and identified to ensure medicine quality by detecting impurities.
Procedure: Precipitation and Observation
- Add 5 drops each of Ag⁺, Pb²⁺, and Hg₂²⁺ solutions into separate test tubes.
- Add 2-3 drops of 2N HCl to each; observe precipitate colors: silver (greenish yellow), lead (colorless to slightly yellow), mercurous (colorless to yellow).
- Boil with 5 drops of water; AgCl is insoluble, PbCl₂ is soluble in hot water, Hg₂Cl₂ is insoluble.
Confirmatory and Solubility Tests
- Add 5 drops of 6N ammonium hydroxide (NH₄OH):
- Silver: white precipitate soluble in excess NH₄OH.
- Lead: chalky white precipitate, insoluble in excess NH₄OH.
- Mercurous: black precipitate, insoluble in excess NH₄OH.
- Add 6N NaOH:
- Silver: brown precipitate, does not dissolve in excess NaOH.
- Lead: white precipitate, dissolves in excess NaOH.
- Mercurous: black precipitate, dissolves in excess NaOH.
Confirmatory Reagents
- Add potassium chromate:
- Silver: red precipitate.
- Lead: yellow precipitate.
- Mercurous: brown precipitate.
- Add potassium iodide:
- Silver: yellow precipitate, dissolves in excess KI.
- Lead: yellow precipitate, dissolves in excess KI.
- Mercurous: green to yellow precipitate, turns black with excess KI.
Importance & Application
- Differentiating ions relies on color, solubility, and reactions with specific reagents.
- Identifying these cations is vital in pharmaceutical analysis to detect and separate impurities.
Key Terms & Definitions
- Cation — positively charged ion.
- Precipitate — solid formed from a solution during a chemical reaction.
- Solubility — the ability of a substance to dissolve in a solvent.
- Qualitative Analysis — process of identifying the components in a mixture.
Action Items / Next Steps
- Study and memorize the observation table for each reagent and cation.
- Review all steps and results in preparation for the exam on Tuesday.