Final answer:
Hydrogen sulfide gas evolves when sulfide ions are introduced into an aqueous solution due to a chemical reaction producing this toxic gas, which has a foul odor similar to that of rotten eggs.
Step-by-step explanation:
When a sulfide ion is introduced into an aqueous solution in a lab setting, hydrogen sulfide gas (H₂S) typically evolves, which is known for its foul smell reminiscent of rotten eggs. This occurs due to particular chemical reactions where sulfide ions react with water (H₂O) to form hydrogen sulfide gas. The reaction can be represented as follows: S²−(aq) + H₂O(l) ⇒ HS−(aq) + OH−(aq) and HS−(aq) + H₂O(l) = H₂S(g) + OH−(aq). Hydrogen sulfide is a weak, diprotic acid that, when dissolved in water, forms hydrosulfuric acid, which further ionizes in two stages producing H₂S gas in the process.
This gas is quite toxic and can be deceptive because it paralyzes the olfactory nerves; hence, after initial exposure, a person may no longer smell it despite its presence. Labs often employ protective measures, such as fume hoods, to manage and contain its release to ensure safety.