Chemical Tests

Flame tests are used to identify certain metal ions in compounds.
In a flame test, a clean platinum or nichrome wire is dipped into a sample and then placed in a flame.
The flame will change colour depending on the metal ion in the sample.
Some common colours observed in flame tests: lithium (Li) turns flame crimson red, sodium (Na) - yellow, potassium (K) - lilac, calcium (Ca) - orange-red, barium (Ba) - green, and copper (Cu) - blue-green.

Sodium hydroxide (NaOH) reacts with many metal ions to form insoluble hydroxides.
This can be used to help identify the metal ion in an unknown sample.
Aluminium (Al), calcium (Ca), and Magnesium (Mg) produce a white precipitate, and iron (II) and iron (III) form green and brown precipitates respectively.
Copper (Cu) ions produce a blue precipitate, zinc (Zn) - a white precipitate, and lead (Pb) - a white precipitate which dissolves in excess NaOH.

To test for ammonium ions (NH4+), heat the sample with sodium hydroxide solution.
If ammonium ions are present, ammonia gas (NH3) will be released.
The ammonia can be detected by its characteristic strong, pungent smell.
Also, it turns damp red litmus paper blue.

To test for a carbonate, add dilute acid to the sample.
If carbonate ions are present, the reaction will produce carbon dioxide gas that can be tested with limewater which turns cloudy due to formation of calcium carbonate.

To test for a sulfate, add dilute hydrochloric acid and barium chloride solution to the sample.
If sulfates are present, a white precipitate of barium sulfate will form.

To test for halide ions (Cl-, Br-, I-), add dilute nitric acid and silver nitrate solution to the sample.
Chlorides, bromides, and iodides will form a precipitate with colours white, cream, and yellow respectively.

Chlorine water bleaches damp litmus paper, bromine water gives orange solution, iodine solution forms a blue-black complex with starch.

Remember that before any test, the solution should be as pure and as isolated as possible, to avoid false results.