Ammonia Test - Pale Blue
Copper sulfate solution is pale blue and ammonia solution is colourless — neither hints that mixing them produces a solid. A small amount of ammonia is enough of a base to precipitate copper hydroxide out of the copper sulfate, appearing as a pale blue solid suspended in the liquid. This activity stops at that first precipitate, the reaction that shows ammonia acting as a base against a metal salt.
2 steps · Ammonia · Study of Compounds
What you will use
Apparatus
- Flask
Chemicals
- Copper Sulfate Solution
- Ammonia Solution
The steps
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Pour copper sulfate solution into the flask.
Pale blue. This colour belongs to the copper ion in solution.
-
Add a little ammonia solution.
A pale blue precipitate forms and clouds the flask.
What it shows
A small amount of ammonia is a strong enough base to precipitate copper hydroxide from copper sulfate solution: CuSO₄ + 2NH₄OH → Cu(OH)₂↓ + (NH₄)₂SO₄. The pale blue solid is copper hydroxide — a different substance from the pale blue solution it came out of, and proof that ammonia, though a weak base, is still base enough to react with a metal salt.