Give an equation for the reaction of solid sodium bromide with concentrated sulfuric acid to form bromine - AQA - A-Level Chemistry - Question 4 - 2021 - Paper 3

During the reaction, orange/brown fumes of bromine are observed, indicating the formation of bromine gas.

1. Dilute nitric acid is used to remove any unwanted ions that may interfere with the subsequent tests for halides.
2. Aqueous silver nitrate is added to precipitate chloride and iodide ions as silver chloride and silver iodide, respectively. This is crucial for identifying halides in the solution.
3. A dilute solution of ammonia is added to distinguish between silver chloride and silver iodide; silver chloride dissolves in ammonia, while silver iodide does not.

The formation of a pale yellow precipitate indicates the presence of silver iodide, which is less soluble and precipitates in the presence of iodide ions. The excess ammonia dissolves the silver chloride precipitate, confirming its identity as it reacts to form a soluble silver ammine complex while leaving the silver iodide intact.

1. The reaction of chloride ions with silver nitrate can be represented as:

$Ag^+ (aq) + Cl^- (aq) \rightarrow AgCl (s)$

2. In the presence of ammonia, the dissolution of silver chloride can be expressed as:

$AgCl (s) + 2NH_3 (aq) \rightarrow [Ag(NH_3)_2]^+ (aq) + Cl^- (aq)$