Transcript Chemical Identification of Unknown Ionic Compounds

Pathways and Methodology
Created by Jared Mader
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
– Resources
Created by Jared Mader
Cation Identification
• When testing cation, the following methods
may be employed:
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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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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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Chemical Color Identification
• Compounds of some transition metals have
unique color:
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Copper: blue, blue/green
Chromium: green, purplish/green
Iron: pale green, yellow, amethyst
Nickel: green
Cobalt: red
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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
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Flame Tests
• Upon using cue tip dip flame test, color
emission will be:
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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
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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
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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
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Addition of Potassium Iodide
Solution
• Carefully add dilute KI solution to solution
of unknown
– Yellow precipitate: lead
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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
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Addition of HCl Solution
• Carefully add dilute HCl solution to
solution of unknown
– White Precipitate: lead
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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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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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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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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
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
This Site Made Possible by:
• http://www.rjclarkson.demon.co.uk/middle/Inorganic%20i
on%20tests%201999.html
• http://www.wpbschoolhouse.btinternet.co.uk/page13/Chem
icalTests/ChemicalTests.htm
• http://www.rod.beavon.clara.net/prelim.htm
• http://www.rod.beavon.clara.net/cations.htm
• http://www.rod.beavon.clara.net/anions.htm
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