8.3.4 Halides

Halides are a group of ions that are derived from halogens, including chloride (Cl^-), bromide (Br^-), and iodide (I^-). One common methodHow a writer presents perspective or viewpoint through language/structure. to test for the presence of halides is by using silver nitrate (AgNO₃) solution in the presence of dilute nitric acid (HNO₃). This test is known as the silver nitrate test for halides.

When silver nitrate solution is added to a solution containing halide ions, a precipitationWhere a solid forms from a liquid solution, often by the addition of another substance. reaction occurs. The silver ions (Ag⁺) from the silver nitrate react with the halide ions to form insoluble silver halide precipitates. The colour of the precipitates depends on the specific halide ion present. The reactions between halide ions and silver nitrate can be represented as follows:

Chloride ion (Cl^-) reacts with silver nitrate to form silver chloride (AgCl) as a white precipitate:

Cl^- (aq) + AgNO₃ (aq) → AgCl (s) + NO₃^- (aq)

Bromide ion (Br^-) reacts with silver nitrate to form silver bromide (AgBr) as a cream-coloured precipitate:

Br^- (aq) + AgNO₃ (aq) → AgBr (s) + NO₃^- (aq)

Iodide ion (I^-) reacts with silver nitrate to form silver iodide (AgI) as a yellow precipitate:

I^- (aq) + AgNO₃ (aq) → AgI (s) + NO₃^- (aq)

The characteristic colours of the precipitates formed allow for the identification of halide ions in a solution. Silver chloride is white, silver bromide is cream-coloured, and silver iodide is yellow. These distinct colours help differentiate between different halides in a mixture.

The addition of dilute nitric acid (HNO₃) is necessary in this test to prevent the precipitation of other silver salts that could interfere with the observation of the specific halide precipitates.