GCSE OCR Gateway C4:1 a-b Halide ion chemical test.

To recall the simple chemical test for halide ions Cl^— (aq),  Br^— (aq) and I^— (aq) in aqueous solution .

The Halogens form a group of non- metals on the right hand side of the Periodic Table Group 7 next to the noble gases.

There are three particular chemical reactions that most courses include.

The reaction of halogens with metals

The reaction of halogens with non – metals

The reaction of halogens with halide ions

Then there is the simple chemical test for halide ions.

The simple chemical test for halide ions: Cl^—_(aq), Br^—_(aq), I^—_(aq).

These are precipitation reactions.

To see if an aqueous salt solution contains halide ions first add a few drops of dilute nitric acid followed by a few drops of 0.05M silver nitrate solution (AgNO₃ (aq)).

The nitric acid is there to remove any other ions particularly carbonate ions that would also form a precipitate with silver nitrate since silver carbonate is a white insoluble solid.

The silver ions in the silver nitrate solution form insoluble precipitates with chlorides, bromides and iodides.

With Chlorides:

Silver nitrate forms a white precipitate with chlorides.

AgNO₃ (aq)    +     NaCl(aq)       ⟶      AgCl(s)       +       NaNO₃ (aq)

                                                                 White ppt

The ionic equation:

Ag+ (aq)    +     Cl^—(aq)        ⟶         AgCl(s)

With Bromides:

Silver nitrate forms a cream precipitate with bromides.

AgNO₃ (aq)    +     NaBr(aq)    ⟶       AgBr(s)       +         NaNO₃ (aq)

                                                              Cream ppt

The ionic equation:

Ag+ (aq)    +     Br^—(aq)       ⟶          AgBr(s)

With Iodides:

Silver nitrate forms a yellow precipitate with iodides.

AgNO₃(aq)    +     NaI(aq)    ⟶             AgI(s)       +      NaNO₃(aq)

                                                               Yellow ppt

The ionic equation:

Ag+ (aq)    +     I^—(aq)     ⟶        AgI(s)

Further confirmatory tests:

If the white precipitate of silver nitrate is added to dilute ammonia solution it should dissolve.

If the cream precipitate of silver bromide is added to concentrated ammonia solution it should dissolve

And yellow silver iodide should be found to be insoluble in ammonia solution.

Effect of bright  sunlight

Lastly, if the three precipitate are exposed to bright light or sunlight then after a few minutes the white precipitate of silver chloride turns dark purple, the bromide turns dark green and the iodide remains yellow.

Summary

The video below shows these tests: