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Tests for ions

The presence of certain ions in an aqueous solution can be detected by making chemical tests.

1) Tests for ions with a precipitation reaction

The presence of certain ions in an aqueous solution can be detected by making chemical tests.
A test for ions is performed in several steps:
- A small part of the tested solution is taken and placed in a test tube.
- A few drops of a chemical called "reactive" are added in this test tube. The reactive is supposed to react with tested ions.

- The result is observed: if the searched ion is present in the solution then a chemical transformation takes place and produces a solid compound which looks a bit like gelatin and that is called "precipitate". Its color must be checked and compared to the expected color.

Example:test for copper ions.

Step 1: some solution is poured in a test tube
Test for ion: copper ion

Step 2: A few drops of an aqueous solution of sodium hydroxide (which acts as a reactive) are added
test for ions: copper ion

Step 3: A blue precipitate forms which confirms the presence of copper ions
Test for ions - precipitation reaction

To realize a test, we must therefore know the reagent to be used and the color of the precipitate that should form.

2) Some tests to know

Ion Iron (II) ion Fe2+ Iron (III) ion Fe3+ Copper ion Cu2+ Chloride ion Cl-
Reactive Sodium hydroxide Sodium hydroxide Sodium hydroxide Silver nitrate
Color of the precipitate Green Red Blue White
(Blackens in the light)

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