Test for Anions
What is an anion?
We will look at
1.
2.
3.
4.
5.
6.
7.
The Chloride Ion ClThe sulfate ion SO42The sulfite ion SO32The carbonate ion CO32The hydrogen carbonate ion HCO3The nitrate ion NO3The phosphate ion PO43-
1. To detect the presence of chloride
ions
Apparatus: 1.Test Tube, 2.Spatula, 3.a chloride salt,
4.silver nitrate, 5.dilute ammonia and 6.deionised water
Procedure
1. Place 2cm3 of water in test tube adding a
small amount of the salt, shaking to dissolve
2. Add a few drops of silver nitrate. What
happens??
3. Add about the same amount of ammonia as
water. What happens?
Chloride ions
Test: Add a few drops of AgNO3 to a solution of
the solid
A precipitate is the name given to
an insoluble material that settles
out of a solution
Observation: A white precipitate is formed
which is soluble in dilute ammonia
Formula:
Ag+ + Cl-  AgCl
The down pointing
arrow means that a
precipitate has formed
2+3: To detect the presence Sulfite and
Sulfate ions
Apparatus: 1.2 test tubes, 2. deionised water, 3.
sulfate salt, 4. sulfite salt, 5. dilute HCl,6. Barium
Chloride
Procedure:
1. Add about 2cm3 of water to both test tubes
and make up a solution of sulfite salt in one
and sulfate in the other, make sure you label
your test tubes!
2. Add a few drops barium chloride to each test
tube to each, note what happens?
Ba2+ + SO42-  BaSO4 ( Barium sulfate)
Ba2+ + SO32-  BaSO3 (Barium sulfite)
How do we distinguish between the 2?
3. Add about 2cm3 of dilute hydrochloric acid to
each test tube
What happens?
Barium sulfate is insoluble in HCl
Barium sulfite is soluble
Sulfate and Sulfite ions
Test: Add BaCl2 solution to the test tubes,
distinguish the two by adding dilute HCl
Observation: A white precipitate is formed,
when HCl is added to this precipitate, if the
precipitate remains : sulfate if it dissolves sulfite
Formulas:
Ba2+ + SO42-  BaSO4 ( Barium sulfate)
Ba2+ + SO32-  BaSO3 (Barium sulfite)
BaSO4 + HCl  No reaction
SO3- + 2H+  SO2 + H2O
4+5: Carbonate and Hydrogen
Carbonate ions
Apparatus: 2 test tubes, carbonate and
hydrogencarbonate salt, dilute HCl, magnesium
sulfate and deionised water
Procedure:
1. Place aprox 1cm of carbonate salt in a test
tube, do the same and add about 2cm3 of acid
into the test tubes. What happens?
Distinguishing between carbonate and
hydrogencarbonate
2. Add Magnesium Sulfate to a fresh solution of
the salt.
Precipitate forms : Carbonate
No precipitate : Hydrogen Carbonate (unless
boiled
Carbonate and Hydrogen Carbonate
Ions
Test: Add dilute HCl to the solids. Distinguish the
two by adding MgSO4 to a fresh solution.
Observation: A gas is given off that turn
limewater milky.
Precipitate forms: Carbonate
No Precipitate: Hydrogencarbonate (precipitate
forms on boiling
Formulas
CO32- + 2H+  CO2 + H2O
HCO3- + 2H+  CO2 + H2O
Reacting with limewater
Ca(OH)2 +CO2  CaCO3 + H2O
Formulas
Reacting with Magnesium Sulfate
Mg2+ + CO32-  MgCO3
Mg2+ + HCO3-  Mg(HCO3)2
With boiling
Mg(HCO3)2  MgCO3 + CO2 + H2O
6. To detect the presence of Nitrate
ions
Apparatus: Test Tube, Nitrate Salt, iron(ii) sulfate,
Concentrated sulfuric acid.
Procedure:
1. Place a small amount of nitrate salt in a test
tube and dissolve with some deionized water.
2. Add the same quantity of freshly prepared
iron(ii) sulfate
3. Carefully add some concentrated sulfuric acid,
VERY DANGEROUS! Note what happens?
Nitrate Ions
Test: Brown Ring Test, To a solution of the solid,
add a freshly prepared FeSO4 solution, add
concentrated sulfuric acid
Observation: A brown ring is formed at the
junction of the 2 liquids
Brown ring is due to the presence of nitrate ion
7. To detect the presence of a
phosphate ion
Apparatus: Test tube, beaker, hot plate, soluble
phosphate salt, ammonium molybdate solution,
concentrated nitric acid, deionized water
Procedure:
1. Add a few crystals of phosphate salt to about 1cm3 of
water and shake to dissolve
2. Pour in ammonium molybdate until the test tube is
half full
3. Add 5 drops of concentrated nitric acid VERY
DANGEROUS! What happens?
7. Phosphate ions
Test: Ammonium molybdate is added to a
solution of the solid. Concentrated nitric acid is
added. Solution id warmed if needed
Observation: Yellow precipitate is formed
Phosphate ions are present