Swap Partners: Displacement Reactions
Watch more reactive elements kick out others.
What this lesson covers
Why it matters
Watch a shiny metal vanish into acid, replaced by bubbles of invisible gas. It is a chemical swap where one element kicks another out of its compound.
The idea in plain words
Balance check: Zn + 2HCl → ZnCl₂ + H₂. Confirm the atom counts match on both sides.
Predict first
What happens when zinc meets dilute hydrochloric acid?
Zinc is more reactive than hydrogen, so it displaces hydrogen from the acid.
- Zinc dissolves and hydrogen gas is released — correct
- Zinc sinks and nothing happens
- The acid turns blue
What you do
Run all three reactions. Observe the gas, the deposit, and the precipitate. Note which element is doing the displacing.
Check yourself
In the reaction Cl₂ + H₂S → 2HCl + S, which element is displaced?
Chlorine is more reactive than sulphur, so it takes the place of sulphur in the compound, leaving elemental sulphur behind.
How do you confirm the gas produced in Zn + 2HCl → ZnCl₂ + H₂ is hydrogen?
Hydrogen is flammable and produces a characteristic 'pop' sound with a burning splinter.
Why does the blue copper sulphate solution turn light green when iron is added?
The colour change indicates the swap: blue copper ions leave the solution, and green iron ions enter it.
- Chlorine
- Sulphur — correct
- Hydrogen
- It turns lime water milky
- A burning splinter pops — correct
- It relights a glowing splinter
- Iron rusts instantly
- Blue Cu²⁺ ions are replaced by green Fe²⁺ ions — correct
- The solution dilutes as it reacts