Amphoteric Metals React
Zinc and aluminium dissolve in both acids and alkalis, releasing hydrogen each time.
What this lesson covers
Why it matters
Most metals react with acids but ignore alkalis. Zinc is a chemical double-agent: it fizzes in dilute acid AND in sodium hydroxide, giving off hydrogen both times. Metals that react with both acids and bases are called amphoteric.
The idea in plain words
Balance aluminium reacting with alkali: aluminium is oxidised and hydrogen is released as sodium aluminate forms.
Predict first
Zinc fizzes in dilute hydrochloric acid, giving off hydrogen. What happens when you drop zinc into sodium hydroxide solution?
Zinc reacts with sodium hydroxide too — warm it and hydrogen bubbles off, forming sodium zincate. A metal that reacts with both acids and bases is amphoteric. Zinc, aluminium and lead behave this way; most metals (like copper) do not.
- It fizzes again, giving off hydrogen — correct
- Nothing — metals never react with bases
- It turns the solution deep blue
- Oxygen gas is released
What you do
An amphoteric metal reacts with BOTH a dilute acid and a hot alkali — releasing hydrogen each time. Run all three reactions and test the gas with a burning splinter.
Check yourself
What does it mean to call a metal amphoteric?
An amphoteric metal (Zn, Al, Pb) shows both acidic and basic behaviour, so it reacts with acids AND with alkalis — releasing hydrogen gas each time.
Zinc reacts with both dilute HCl and hot NaOH. Which gas is given off in BOTH reactions?
Both Zn + 2HCl → ZnCl₂ + H₂ and Zn + 2NaOH → Na₂ZnO₂ + H₂ release hydrogen, which burns with a squeaky pop.
Which of these metals is NOT amphoteric?
Zinc, aluminium and lead are amphoteric — they react with both acids and alkalis. Copper reacts with neither to release hydrogen.
Aluminium also reacts with dilute hydrochloric acid: 2Al + 6HCl → 2AlCl₃ + 3H₂. With 2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂, what does this prove about aluminium?
Reacting with both an acid and an alkali — releasing hydrogen each time — is exactly what makes a metal amphoteric.
- It reacts with both acids and bases — correct
- It reacts only with acids
- It reacts only with bases
- It reacts with neither acids nor bases
- Hydrogen — it pops with a lighted splint — correct
- Oxygen — it relights a glowing splint
- Carbon dioxide — it turns limewater milky
- No gas is released
- Copper — correct
- Zinc
- Aluminium
- Lead
- It is amphoteric — it reacts with both acids and bases — correct
- It is a noble, unreactive metal
- It only reacts when heated
- It is a non-metal