Same acid, different gas
In a school lab, iron in acid gives one gas. Iron sulfide in acid gives another.
Dilute means mixed with a lot of water.
- One dilute acid goes into three tubes.
- Iron gives iron chloride and hydrogen. The gas has no smell. It burns with a pop.
- Iron sulfide gives a different gas: hydrogen sulfide.
- Sulfur does not react with the acid.
A word equation names what goes in and what comes out. The arrow means makes. Hydrochloric acid is a common lab acid.
The rule
A word equation names the substances that go in and come out. Iron and dilute hydrochloric acid make iron chloride and hydrogen. Iron sulfide and the acid make iron chloride and hydrogen sulfide. Sulfur does not react with the acid.
Four samples in dilute hydrochloric acid:
- Iron: no smell. It burns with a pop.
- Iron sulfide: it smells of rotten eggs.
- Iron and sulfur, just mixed: the iron gives hydrogen. Sulfur is left.
- Sulfur: no reaction. No gas.
The word equations for the two gases:
- iron + dilute hydrochloric acid → iron chloride + hydrogen
- iron sulfide + dilute hydrochloric acid → iron chloride + hydrogen sulfide
So the gas, and what is left behind, tell these samples apart.
Hydrogen sulfide is a poisonous gas. A teacher tests it in a room with plenty of fresh air. Even dilute acid needs care. Never smell a gas yourself.
Pick a sample. Add the acid. Match the goal.
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