Tests for negative ions
CARBONATES
Carbonate ions, CO32- can be detected whether in a solid compound or in solution. An
acid, such as dilute hydrochloric acid, is added to the test compound.
Carbon dioxide gas bubbles and zzes if carbonate ions are present. Limewater is used
to con rm that the gas is carbon dioxide. It turns from clear to milky when carbon dioxide
is bubbled through.
HALIDE IONS (CHLORIDES, BROMIDES, AND IODIDES)
You identify halides by adding nitric acid then silver nitrate solution. This produces a
precipitate of silver halide.
- chloride ions give a white precipitate of silver chloride
- Bromide ions give a cream precipitate of silver bromide
- Iodide ions give a yellow precipitate of silver iodide.
TESTING FOR SURFACE IONS
1. Add dilute hydrochloric acid to a sample.
2. Then, add barium chloride solution.
3. This produces a white precipitate of barium sulfate.
Summary questions:
1. List the reagent you would need to assemble in a lab to test a sample of an unknown
substance for carbonate, halide and sulfate ions.
Dilute hydrochloric acid, limewater, dilute nitric acid, silver nitrate solution and barium
chloride solution.
2. An unknown compound is a white solid which dissolves in water to produce a
colorless solution. When this solution is acidi ed with nitric acid and the silver nitrate
is added, a yellow precipitate is produced. A ame test on the unknown compound
produces a lilac ame. Deduce the name of the unknown compound and give your
reasoning.
Potassium iodide. That’s because potassium ions form a lilac ame in a ame test and
silver iodide is formed with silver nitrate solution.
fi fl fi fifl fl fl
CARBONATES
Carbonate ions, CO32- can be detected whether in a solid compound or in solution. An
acid, such as dilute hydrochloric acid, is added to the test compound.
Carbon dioxide gas bubbles and zzes if carbonate ions are present. Limewater is used
to con rm that the gas is carbon dioxide. It turns from clear to milky when carbon dioxide
is bubbled through.
HALIDE IONS (CHLORIDES, BROMIDES, AND IODIDES)
You identify halides by adding nitric acid then silver nitrate solution. This produces a
precipitate of silver halide.
- chloride ions give a white precipitate of silver chloride
- Bromide ions give a cream precipitate of silver bromide
- Iodide ions give a yellow precipitate of silver iodide.
TESTING FOR SURFACE IONS
1. Add dilute hydrochloric acid to a sample.
2. Then, add barium chloride solution.
3. This produces a white precipitate of barium sulfate.
Summary questions:
1. List the reagent you would need to assemble in a lab to test a sample of an unknown
substance for carbonate, halide and sulfate ions.
Dilute hydrochloric acid, limewater, dilute nitric acid, silver nitrate solution and barium
chloride solution.
2. An unknown compound is a white solid which dissolves in water to produce a
colorless solution. When this solution is acidi ed with nitric acid and the silver nitrate
is added, a yellow precipitate is produced. A ame test on the unknown compound
produces a lilac ame. Deduce the name of the unknown compound and give your
reasoning.
Potassium iodide. That’s because potassium ions form a lilac ame in a ame test and
silver iodide is formed with silver nitrate solution.
fi fl fi fifl fl fl
