metal hydroxide test

Sodium hydroxide solution be used to identify some metal ions ( cations ).

Method:

Simply add the substance to sodium hydroxide solution and observe precipitates forming. Aluminium, calcium, magnesium, copper ( II ), iron ( II ) and iron ( III ) ions all form precipitates when combined with NaOH but the colour varies as follows:

Aluminium - white precipitate ( dissolves in excess sodium hydroxide )

Calcium - white precipitate

Magnesium - white precipitate

Copper ( II ) - blue precipitate

Iron ( II ) - green precipitate

Iron ( III ) - brown precipitate

Equation:

Both the symbol and word equation for each reaction follow the same pattern, the the metal displaces the sodium in the sodium hydroxide and forms a new metal hydroxide and sodium chloride/sulfate.

E.g coppers equations are:

Copper sulfate + sodium hydroxide —> copper hydroxide + sodium sulfate

CuSO*4 ( aq) + 2NaOH ( aq ) —> Cu(OH)*2 ( s ) + 2Na*2SO*4

Problems are same as flame tests