Metal Clash: HCl
React HCl with active metals to release H2
What this lesson covers
Why it matters
A strip of magnesium vanishes in acid, leaving behind bubbles that sing when a flame touches them. It is not magic; it is a violent swap of partners.
The idea in plain words
Balance the equation: Mg + 2HCl → MgCl₂ + H₂. Confirm the 1:2:1:1 ratio.
Predict first
What gas escapes when magnesium meets dilute hydrochloric acid?
Metals above hydrogen in the reactivity series displace hydrogen from acids, releasing H₂ gas.
- Chlorine gas
- Hydrogen gas — correct
- Carbon dioxide
- Oxygen gas
What you do
Test all three metals. Note the speed of fizzing and the final solution colour.
Check yourself
Which observation confirms the gas is hydrogen?
Hydrogen is highly flammable; the 'pop' test is its definitive identification.
Why does iron react slower than magnesium with HCl?
Magnesium stands higher than iron in the activity series, so it displaces hydrogen far more vigorously.
What is the colour of the solution after iron reacts with dilute HCl?
Iron displaces hydrogen to form Ferrous Chloride (FeCl₂), which is green in solution.
- It turns lime water milky
- A burning splinter produces a 'pop' sound — correct
- It relights a glowing splinter
- It turns blue litmus red
- Iron is less reactive than magnesium — correct
- Iron is heavier
- Iron forms a protective oxide layer instantly
- Magnesium is magnetic
- Green — correct
- Blue
- Yellow
- Colourless