Flame Tests for Positive Ions
Tests for metal ions. When some of these elements are put in a flame, colours are produced:
Flame Tests for Positive Ions, Metal Hydroxides
When sodium hydroxide is added to metal hydroxides, a precipitate can form:
Aluminium, calcium and magnesium ions form white precipitates. Aluminium hydroxide dissolves when excess sodium hydroxide is added.
Copper(II) hydroxide is blue.
Iron(II) hrdroxide is green and slowly turns brown.
Iron(III) hydroxide is reddish brown.
Tests for Negative Ions, Carbonate Ions
Add dilute hydrochloric acid to the substance to see if it fizzes. If it does and the gas produced turns lime water milky, the substance contains carbonate ions.
Tests for Positive Ions, Halide Ions
Add dilute nitric acid and then silver nitrate and a precipitate is produced.
Tests for Negative Ions, Sulfate Ions
Add dilute hydrochloric acid and then barium chloride solution. If a white precipitate forms, sulfate ions are present.
Tests for Negative Ions, Nitrate Ions
Add a little aluminium powder and then sodium hydroxide solution. Gently warm and test the gas given off with damp red litmus paper. If it turns blue, ammonia was produced and nitrate ions are present.
Tests for Negative Ions, Metal Carbonates
Carbonates also produce carbon dioxide when they decompose on heating but can be more difficult to detect.
Copper carbonate is green and when heated it decomposes to form black copper oxide.
Zinc carbonate is white and decomposes to form zinc oxide, which is yellow when hot but turns white when cool.
Testing for Organic Substances
All organic compounds contain carbon. Many organic compounds burn when heated in air and produce carbon dioxide. Those that do not burn usually blacken or char showing that they contain carbon.