SC25 Qualitative analysis: tests for ions mind map

Planning / flames

• Qualitative: Identify substance, not quantity; combine distinctive observations
• Separate samples: Clean tools / references prevent contamination and misleading results
• Flame colours: Li red; Na yellow; K lilac; Ca orange-red; Cu blue-green
• Meaning / safety: Flame identifies cation, not anion; precise observations / controls

NaOH cation tests

• Method: Add dropwise, then excess where needed; observe insoluble precipitate
• White: Al³⁺ dissolves in excess NaOH; Ca²⁺ remains
• Coloured: Cu²⁺ blue; Fe²⁺ green; Fe³⁺ red-brown; record promptly
• Ammonium: Warm with NaOH → NH₃; damp red litmus turns blue
• Equation / limits: Cu²⁺ + 2OH⁻ → Cu(OH)₂; combine tests within specified set

Anion tests

• Carbonate: Dilute acid → gas; limewater cloudy confirms CO₂
• Sulfate: Dilute HCl then BaCl₂ → white BaSO₄ precipitate
• Halides: Dilute HNO₃ then AgNO₃: Cl white / Br cream / I yellow
• Avoid HCl: It introduces Cl⁻ into halide test → false positive
• Salt identity: Core practical combines cation / anion; separate portions / controls
• Net equations: Ag⁺ + Cl⁻ → AgCl; Ba²⁺ + SO₄²⁻ → BaSO₄

Instruments

• Sensitivity: Fast / small concentrations; calibration / clean samples still needed
• Flame photometry: Reference signals identify; known standards → concentration curve
• Within range: Interpolate; dilute concentrated sample / apply dilution factor
• Check quality: Blank checks background; repeats; do not assume universal linearity
• Evaluate: Sensitivity, accuracy, speed, cost / interference / training

Connections

• Planning / flames → Anion tests: Identifying a salt requires both cation and anion evidence.
• Planning / flames → Instruments: Visual identification and calibrated instruments answer different measurement needs.