Acts like both
Amphoteric oxides.
Acid or base?
Most metal oxides are basic. Aluminium oxide is different.
How might aluminium oxide behave with an acid and with a base?
What this lesson covers
The idea
Metal oxides that react with both acids and bases to produce salts and water, showing acidic as well as basic behaviour, are amphoteric oxides; aluminium oxide and zinc oxide are amphoteric.
Acid or base?
Most metal oxides are basic. Aluminium oxide is different.
How might aluminium oxide behave with an acid and with a base?
- It reacts with both
- It reacts with neither
- It reacts with acids only
Two reactions
Press Next step. A teacher does such reactions in the lab; here we only watch.
Acidic and basic behaviour
Most metal oxides are basic and react with acids. A few, such as aluminium oxide and zinc oxide, show both acidic and basic behaviour. They react with acids and with bases, giving a salt and water each time. They are called amphoteric oxides.
Metal oxides that react with both acids and bases to produce salts and water, showing acidic as well as basic behaviour, are amphoteric oxides; aluminium oxide and zinc oxide are amphoteric.
Notes
Amphoteric oxides react with both acids and bases to give salts and water: aluminium oxide and zinc oxide.
Check yourself
Which pair of oxides is amphoteric?
An amphoteric oxide reacts with ...
What do the reactions of aluminium oxide with HCl and with NaOH both produce?
Aluminium oxide reacts with sodium hydroxide (NaOH) to give water and ...
- Copper(II) oxide and sodium oxide. The book gives copper(II) oxide as an ordinary basic oxide; the amphoteric ones named are aluminium oxide and zinc oxide.
- Magnesium oxide and potassium oxide. The book names aluminium oxide and zinc oxide as the amphoteric oxides.
- Aluminium oxide and zinc oxide — correct. Yes!
- both acids and bases — correct. Yes!
- acids only. An amphoteric oxide reacts with bases too.
- bases only. An amphoteric oxide reacts with acids too.
- A salt and hydrogen gas. Hydrogen is formed when a metal reacts with an acid; the oxide reactions in the book give a salt and water.
- A salt and water — correct. Yes!
- Water alone. A salt is also formed in each reaction: aluminium chloride with HCl, sodium aluminate with NaOH.
- sodium chloride. Sodium chloride (NaCl) is not formed here; the salt is NaAlO₂.
- aluminium metal. The reaction gives a salt, sodium aluminate, not the metal.
- sodium aluminate — correct. Yes!