Common Laboratory Tests

Chemistry, Schools 12 161

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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