1. Pathways and Methodology
Chemistry Crisis
Pathways and Methodology
Created by Jared Mader

2. Chemical Identification
The tests found in the identification methods listed below will help you identify the unknown chemicals used by the food manufacturer:
Cation Identification
Anion Identification
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3. Cation Identification
When testing cation, the following methods may be employed:
Chemical Color Identification
Solubility
Flame Test for Identification
Addition of sodium hydroxide solution
Addition of ammonia solution
Addition of potassium iodide solution
Ammonium Identification
Addition of Hydrochloric Acid
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4. Anion Identification
When testing anion, the following methods may be employed:
Addition of silver nitrate to a slightly acidic solution of compound
Addition of sulfuric acid*
Polyatomic anion tests
Addition of Lead(II) Nitrate
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5. Chemical Color Identification
Compounds of some transition metals have unique color:
Copper: blue, blue/green
Chromium: green, purplish/green
Iron: pale green, yellow, amethyst
Nickel: green
Cobalt: red
• Students must realize that this is only a starting point to guide more testing.
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6. Solubility The following are insoluble: Halides of lead and silver
Sulfates of barium, calcium, strontium, and lead
Carbonates of all metals with the exception of alkali metals
• Students must realize that this is only a starting point to guide more testing.
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7. Flame Tests Upon using cue tip dip flame test, color emission will be:
Sodium: bright yellow/orange
Potassium: lilac
Strontium/Lithium: bright red
Barium: pale green
Calcium: brick/orange red
Copper: green with blue/white center
Lead: Whitish in color
• Prior laboratory involving the teaching of the Flame Test Method must be completed.
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8. Sodium Hydroxide Addition
Carefully add dilute NaOH solution to solution of unknown
White precipitate: calcium, zinc, strontium, aluminum, and lead
Blue precipitate, but turns black upon heating: copper
Green precipitate: Nickel
Gray/green, turning brown on standing: Iron(II)
Red precipitate: Iron(III)
Blue precipitate, turning gray upon standing: Cobalt
• 1M stock solution of NaOH should be prepared by teacher and placed in dropper bottles.
• Litmus paper must be available
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9. Ammonia Solution Addition
Carefully add dilute NH3 solution to solution of unknown
White precipitate: calcium, aluminum, lead, and zinc
Blue precipitate, turning to deep blue solution as more NH3 is added : copper
Coral Blue Solution: nickel
Gray/green, turning brown on standing: Iron(II)
Red precipitate: Iron(III)
Blue precipitate, turning gray upon standing: Cobalt
• Stock solution of ammonia must be prepared and stored in labeled dropper bottles.
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10. Addition of Potassium Iodide Solution
Carefully add dilute KI solution to solution of unknown
Yellow precipitate: lead
• Potassium iodide solution must be prepared and stored in labeled dropper bottles.
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11. Addition of Potassium Chromate Solution
Carefully add dilute potassium chromate solution to solution of unknown
Fine crystalline precipitate: zinc, cobalt, iron(III), nickel, or lead
• Potassium iodide solution must be prepared and stored in labeled dropper bottles.
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12. Addition of HCl Solution
Carefully add dilute HCl solution to solution of unknown
White Precipitate: lead
• Potassium iodide solution must be prepared and stored in labeled dropper bottles.
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13. Addition of Silver Nitrate
Carefully add a dilute AgNO3 solution to a slightly acidic solution of unknown
Create slightly acidic solution by adding several drops of HNO3
White precipitate: chloride
Cream precipitate: bromide
Yellow precipitate: iodide
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14. Addition of Sulfuric Acid
*MUST BE CONDUCTED IN FUME HOOD
Carefully add several drops of concentrated sulfuric acid to solution of unknown
Brown acidic fumes: bromide or nitrite
Purple acidic fume: iodide
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15. Addition of Lead(II) Nitrate
Carefully add several drops of lead(II) nitrate solution to a solution of unknown
Yellow precipitate: iodide
White precipitate: bromide, chloride or sulfate
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16. Polyatomic Ion Tests
To a solution of the unknown, carefully add several drops of:
COLD NaOH = strong ammonia smell and litmus turns red to blue = ammonium ion
Dilute solution of potassium permanganate and HCl = turns from purple to clear = nitrite ion
Ammonium solution = strong ammonia smell, no precipitate and litmus turns red to blue = hydroxide ion
If soluble, add AlNO3 solution = white precipitate = hydroxide ion
Heat solid in a test tube with a burner = brown gas(nitrogen dioxide) = nitrate ion [MUST COMPLETE IN FUME HOOD]
HCl and BaCl2 = white precipitate = sulfate ion
Dilute HCl = vigorous bubbling of CO2 gas = carbonate ion
Gently heat solid = color change/release of CO2 = carbonate ion
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Created by Jared Mader

17. Polyatomic Ion Tests
To a solution of the unknown, carefully add several drops of:
COLD NaOH = strong ammonia smell and litmus turns red to blue = ammonium ion
Dilute solution of potassium permanganate and HCl = turns from purple to clear = nitrite ion
Ammonium solution = strong ammonia smell, no precipitate and litmus turns red to blue = hydroxide ion
If soluble, add AlNO3 solution = white precipitate = hydroxide ion
Heat solid in a test tube with a burner = brown gas(nitrogen dioxide) = nitrate ion [MUST COMPLETE IN FUME HOOD]
HCl and BaCl2 = white precipitate = sulfate ion
Dilute HCl = vigorous bubbling of CO2 gas = carbonate ion
Gently heat solid = color change/release of CO2 = carbonate ion
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Created by Jared Mader

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