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You are here: Home / Chemistry / Common Laboratory Tests

Common Laboratory Tests

May 1, 2007 By Hiran Leave a Comment

    This is a list of some qualitative laboratory tests that can be used to identify unknowns in lab. These are simple tests leading to the identification of a few anions and cations and some common gases. Also included here is flame test information for selected cations.

    Tests for anoins

    Anion Symbol
    Test
    Results
    Bromide
    Br-
    Add silver nitrate solution to a solution of substance in dilute nitric acid Pale yellow precipitate, dissolves slightly in ammonia solution.
    Carbonate
    CO32-
    a)Add dilute hydrochloric acid to the substance.b)Add drop of phenolphthalein to a solution of substance. Carbon dioxide gas is given off.
    Turns bright pink (HCO3 turns light pink).
    Chloride
    Cl-
    Add silver nitrate to a solution of substance in dilute nitric acid. Thick white precipitate dissolves in ammonia solution.
    Hydrogen-
    carbonate
    HCO32-
    a)Add dilute hydrochloric acid to the substance.b)Add drop of phenolphthalein to a solution of substance. Carbon dioxide gas is given off.
    Turns light pink (CO32- turns bright pink).
    Iodide
    I-
    Add silver nitrate to a solution of substance in dilute nitric acid. Pale yellow precipitate, does not dissolve in ammonia solution.
    Nitrate
    NO3-
    Add iron(II) sulfate solution followed by concentrated sulfuric acid to the solution Brown ring forms at the junction of the two liquids.
    Sulfate
    SO42-
    Add solution of barium chloride to the solution. White precipitate, does not dissolve in dilute hydrochloric acid.
    Sulfite
    SO32-
    Add solution of barium chloride to the solution. White precipitate, does dissolve in dilute hydrochloric acid.
    Sulfide
    S2-
    Add lead(II) ethanoate solution to the solution. Black precipitate

    Tests for cations

    Cation Symbol
    Test
    Results
    Aluminum
    Al3+
    a)Add dilute sodium hydroxide solution to a solution of the substance.b)Add dilute ammonia solution to a solution of the substance. White precipitate that dissolves as more sodium hydroxide solution is added.
    White precipitate that does not dissolve as more ammonia solution is added.
    Ammonium
    NH4+
    Add sodium hydroxide solution to a solution of the substance and gently heat. Ammonia gas is given off.
    Calcium
    Ca2+
    Add dilute sulfric acid to a solution of the substanceAlso try flame test White precipitate formed.
    Copper (II)
    Cu2+
    a) Add dilute sodium hydroxide solution to a solution of the substance.b) Add dilute ammonia solution to a solution of the substance.Also try flame test Pale blue precipitate that dissolves as more sodium hydroxide is added.Pale blue precipitate, changing to deep blue solution as more ammonia is added.
    Iron(II)
    Fe2+
    a) Add dilute sodium hydroxide solution to a solution of the substance.b) Add dilute ammonia solution to a solution of the substance. Pale green precipitate formed.
    Pale green precipitate formed.
    Iron(III)
    Fe3+
    a) Add dilute sodium hydroxide solution to a solution of the substance.b)Add dilute ammonia solution to a solution of the substance. Red-brown precipitate formed.
    Red-brown precipitate formed.
    Lead(II)
    Pb2+
    a)Add dilute sodium hydroxide solution to a solution of the substance.b)Add dilute ammonia solution to a solution of the substance.Use flame test to distinguish between lead and aluminum. White precipitate, that does dissolve as more sodium hydroxide is added.White precipitate that does not dissolve as more ammonia is added.
    Magnesium
    Mg2+
    a) Add dilute sodium hydroxide solution to a solution of the substance.
    b) Add dilute ammonia solution to a solution of the substance.
    White precipitate, that does not dissolve as more sodium hydroxide is added.White precipitate that does not dissolve as more ammonia is added.
    Zinc
    Zn2+
    a) Add dilute sodium hydroxide solution to a solution of the substance.b) Add dilute ammonia solution to a solution of the substance. White precipitate, that dissolve as more sodium hydroxide is added.White precipitate that dissolve as more ammonia is added.

    Flame test for cations

     

    Metal Symbol
    Flame Color
    Barium
    Ba
    Yellow-green
    Calcium
    Ca
    Red
    Copper
    Cu
    Green
    Lead
    Pb
    Blue
    Lithium
    Li
    Pink
    Potassium
    K
    Lilac
    Sodium
    Na
    Orange

    Tests for some common gases

     

    Gas Symbol
    Test
    Results
    Carbon dioxide
    CO2
    bubble gas through limewater (calcium hydroxide solution) Turns limewater cloudy.
    Hydrogen
    H2
    Put a lighted splint into a sample of the gas. Burns with a “popping” sound
    Oxygen
    O2
    Put a glowing splint into a sample of the gas. Splint relights.


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