Give an equation for the reaction of solid sodium iodide with concentrated sulfuric acid to form hydrogen sulfide ($H_{2}S$) and iodine ($I_2$).

State one observation made during this reaction.

A solution that is thought to contain chloride ions and bromide ions is tested.

1. Dilute nitric acid is added to the solution.
2. Aqueous silver nitrate is added to the solution.
3. A cream-coloured mixture of precipitates forms.
4. Excess dilute aqueous ammonia is added to the mixture.
5. Some of the precipitate dissolves and a cream-coloured precipitate remains.

Give a reason for the use of each reagent (nitric acid, silver nitrate, and dilute ammonia).

Explain the observations.

Give ionic equations for any reactions.