Metal oxides act like bases

The idea

Metal oxides react with acids to give a salt and water, like a base does, so metallic oxides are basic oxides.

Black powder meets acid

Copper oxide is a black powder. A teacher warms it gently with dilute hydrochloric acid.

What do you expect?

• The powder dissolves and the liquid turns blue-green
• Hydrogen bubbles fizz out
• Nothing happens

Oxide plus acid

A teacher does this in the lab. Warm each oxide with dilute HCl.

Now compare it with a base meeting an acid.

The oxide is the base’s twin

Metal oxides react with acids to give a salt and water, like a base does. So metallic oxides are basic oxides.

Metal oxide + Acid → Salt + Water

• Reactants | Products
• Base + acid | NaOH + HCl | NaCl + H₂O
• Metal oxide + acid | CuO + 2HCl | CuCl₂ + H₂O

Notes

Metal oxides react with acids to give a salt and water, like a base does, so metallic oxides are basic oxides.

Check yourself

Copper oxide is warmed with dilute HCl. What forms?

Metal oxide + Acid → ?

Why are metallic oxides called basic oxides?

MgO + 2HCl → ? + H₂O. What is the salt?

• Copper and hydrogen. A metal oxide gives a salt and water, not hydrogen.
• Copper(II) chloride and water — correct. Yes! A salt and water.
• Copper(II) chloride and hydrogen. There is no free metal here, so no hydrogen. A salt and water form.
• Salt + hydrogen. That is metal + acid.
• Salt + carbon dioxide + water. That is carbonate + acid.
• Salt + water — correct. Yes!
• They react with acids to give salt and water, as a base does — correct. Yes!
• They turn red litmus red. A base turns red litmus blue. The idea is about reacting with acids.
• They dissolve every metal. That is not what makes them basic.
• MgH₂. The salt joins magnesium with the chloride part of the acid.
• MgCl₂ — correct. Yes! Magnesium chloride.
• MgO₂. The oxygen goes to the water. The salt is MgCl₂.