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Quantitative analysis: tests for ions Typeit
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tests can be used to identify cations by their distinctive colours while burning in a Bunsen burner, e.g. sodium ions burn , potassium ions burn and copper ions burn . Precipitates of different colours may also form when cations react with sodium hydroxide. Calcium and aluminium ions form precipitates, although only the precipitate dissolves when more sodium hydroxide is added. Copper(II) forms a precipitate, while iron(II) is green and iron(III) is brown.
Anions can also be tested for in a range of qualitative tests, e.g. ions give off carbon dioxide when a dilute acid is added, and form precipitates of different colours when silver nitrate is added in the presence of dilute . Iodide goes yellow, goes cream and goes white.
These qualitative tests must have unique results to be useful in identifying ions. However, instrumental methods, such as flame , have many benefits over chemical methods, such as being more accurate and reliable.