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Science

Analysis of ionic compounds

Anion tests

Particular ions present in solution in water can be detected by precipitation reactionsprecipitation reaction: A reaction in which an insoluble solid is formed when certain solutions are mixed..

Testing for the sulfate ion

You can test to see if a solution contains sulfate ions by using barium chloride. If barium chloride solution is added to a sample of water containing sulfate ions, barium sulfate is formed. Barium sulfate is insoluble in water, and will be seen as a white precipitate.

Barium chloride solution + sodium sulfate solution → sodium chloride solution + solid barium sulfate

Testing for halide ions

Barium sulfate

A test using silver nitrate

The halogens are the elements in group 7 of the periodic table, like chlorine, bromine and iodine. Their ions are called halide ions.

You can test to see if a solution contains chloride, bromide or iodide ions by using silver nitrate. If silver nitrate solution is added to a sample of water containing halide ions the silver halide is precipitated. This is because the silver halides are all insoluble in water.

The results look like this:

  • Silver chloride is a white precipitate
  • Silver bromide is a cream precipitate
  • Silver iodide is a pale yellow precipitate

For example:

Silver nitrate solution + sodium bromide solution → sodium nitrate solution + solid silver bromide

Testing for carbonate ions

Limewater is used to test for the presence of carbonate ions (CO32-). Acid is added to the test compound. If carbonate ions are present then carbon dioxide gas bubbles off. If this is passed through limewater is turns the limewater from clear to cloudy.

Back to Ionic compounds and analysis index

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