For example, copper sulfate solution reacts with a few drops of sodium hydroxide solution:
copper sulfate + sodium hydroxide → sodium sulfate + copper hydroxide
CuSO4(aq) + 2NaOH(aq) → Na2SO4(aq) + Cu(OH)2(s)
Copper hydroxide forms a blue precipitate.
The table shows the coloured precipitates formed by five common metal ions.
|Metal ion||Precipitate colour|
Distinguishing between calcium ions and zinc ions
A few drops of dilute sodium hydroxide solution react to form a white precipitate with calcium ions and with zinc ions. However, if excess sodium hydroxide solution is added:
A green precipitate forms when dilute sodium hydroxide solution is added to a sample in solution. Identify the metal ion present in the original solution.
Iron(II) ions, Fe2+, are present.