This is a simple test tube test to detect halide ions.
- the unknown halide substance is dissovled in water
- an aqueous solution of silver nitrate (AgNO3 (aq) is added
- the silver (Ag+) ions from the silver nitrate react with any halide ions that are present, froming a silver halide precipitate, AgX (s)
- These precipitates are coloured, each colour being specific to one halide.
Test (part 2)
Sometimes it is hard to tell the difference between the coloured silver halide precipitates. If this is the case there is another part to the test
- if you are unsure, then add aqueous ammonia, NH3 (aq)
- different halides precipitates have different soluabilities in aqeous ammonia - this can then confirm which halide ion is present.
Halide test results are:
- Chloride= white precipitate, soluble in dilute aqueous ammonia
- Bromide= cream precipitate, soluble in concentrated aqueous ammonia
- Iodide= yellow precipitate, insoluble in concentrated aqueous ammonia
You also need to know the ionic equations for each reaction
- Chloride = Ag+ (aq) + Cl- (aq) --> AgCl (s)
- Bromide = Ag+ (aq) + Br- (aq) --> AgBr (s)
- Iodide = Ag+ (aq) + I- (aq) --> AgI (s)
This type of reaction is called a precipitate reaction.
A Precipitate reaction is the formation of a solid from a solution during a chemical reaction. Precipitates are often formed when two aqueous solutions are mixed together.