Sequential Testing Strategy

📋 Sequential Testing Strategy

When identifying an unknown compound, follow this logical order:

1. Observe: Note colour, state, and any obvious properties
2. Flame test first: Quick visual check for Li⁺, Na⁺, K⁺, Ca²⁺, Cu²⁺
3. NaOH test: For transition metal cations and Al³⁺, Ca²⁺
4. Add dilute HCl: Does it fizz? If yes, CO₃²⁻ is present
5. BaCl₂ + HCl: White precipitate = SO₄²⁻
6. AgNO₃ + HNO₃: White/cream/yellow precipitate identifies Cl⁻/Br⁻/I⁻
7. Confirm identity: Check that cation + anion combination is chemically sensible

Example: Identifying an Unknown White Solid

1. Flame test → red flame (suggests Ca²⁺ or Li⁺)
2. Add acid → fizzing; gas turns limewater milky → CO₃²⁻ present
3. NaOH → white precipitate that does NOT redissolve (confirms Ca²⁺, not Al³⁺)
4. Conclusion: Calcium carbonate (CaCO₃)