Metals and Non-metals · Lesson 3 of 13
Chemical Properties Of Metals: Reaction With Oxygen
“Metals meet oxygen, and their oxides reveal just how reactive they really are.”
• Explain how metals react with oxygen to form metal oxides. • Distinguish basic and amphoteric metal oxides. • Write and interpret equations for copper and aluminium oxidation. • Explain why sodium and potassium are stored in kerosene and why some metals resist further oxidation. • Explain anodising as formation of a thicker protective oxide layer on aluminium.
Chemical behaviour provides a clearer comparison of metals than physical appearance alone. Oxygen is a useful starting point because almost all metals can form oxides, but the reactions occur with very different vigour.
Chemical Properties Of Metals
What Happens When Metals Are Burnt In Air?
Copper does not normally burn with a flame, but hot copper forms a black coating of copper(II) oxide.
Aluminium reacts with oxygen to form aluminium oxide.
Basic Metal Oxides
Most metal oxides are basic in nature. However, aluminium oxide and zinc oxide can react with both acids and bases.
Amphoteric Oxides
An Amphoteric Oxide reacts with both acids and bases to form salt and water.
Aluminium oxide and zinc oxide show both acidic and basic behaviour.
Metal Oxides Forming Alkalis
Most metal oxides are insoluble in water, but sodium oxide and potassium oxide react with water to produce alkalis.
Different Reactivities Towards Oxygen
Potassium and sodium react so vigorously that they can catch fire in the open, so they are stored in kerosene. Magnesium reacts less vigorously. Iron does not normally burn as a bulk piece, but iron filings burn readily in a flame. Copper forms black copper(II) oxide, while silver and gold do not react with oxygen even at high temperatures.
Protective Oxide Layers
Magnesium, aluminium, zinc and lead can form thin oxide layers at ordinary temperature. The layer can reduce further oxidation by separating the underlying metal from the surroundings.
Anodising
Anodising is a process used to form a thicker protective oxide layer on aluminium.
During anodising, a clean aluminium article is made the anode and electrolysed in dilute sulphuric acid. Oxygen formed at the anode reacts with aluminium and creates a thicker oxide layer, increasing corrosion resistance. The oxide coating can also be dyed.
Quiz
What is the usual product when a metal reacts with oxygen?
Which pair contains amphoteric oxides?
Why are sodium and potassium kept in kerosene?
What colour coating forms on heated copper?
What is the purpose of anodising aluminium?
Practice Problems
- Write and balance the equations for copper and aluminium reacting with oxygen.
- Define amphoteric oxide and use both aluminium oxide reactions to justify the definition.
- Explain why sodium and potassium are stored under kerosene while silver and gold can remain exposed to air.
- Explain how a thin oxide layer can reduce further oxidation.
- Describe anodising and explain how it improves aluminium.
- Compare bulk iron and iron filings in a flame and explain why their behaviour can differ.
Key Takeaways
• Metals generally react with oxygen to form metal oxides. • Most metal oxides are basic, while aluminium oxide and zinc oxide are amphoteric. • Sodium and potassium react extremely vigorously and are stored in kerosene. • Some metals form protective oxide layers that slow further oxidation. • Anodising deliberately thickens the protective aluminium oxide layer.