Metals Burn to Oxides
Metals join with oxygen to make basic oxides.
What this lesson covers
Why it matters
Hold magnesium ribbon in a flame and it blazes with a dazzling white light. What is left behind is a soft white powder — the metal has swallowed oxygen from the air.
Predict first
When magnesium burns in air, what substance is formed?
Magnesium combines with oxygen to form magnesium oxide: 2Mg + O₂ → 2MgO. The white powder left behind is the metal oxide.
- Magnesium oxide — correct
- Magnesium hydroxide
- Pure magnesium metal
- Magnesium sulphide
What you do
Burn magnesium ribbon in oxygen and watch it form a white oxide: 2Mg + O₂ → 2MgO. Then dissolve the powder and test it with red litmus.
Check yourself
What is the general product when a metal reacts with oxygen?
The general rule is: metal + oxygen → metal oxide. Magnesium gives magnesium oxide, and iron gives iron oxide.
When magnesium oxide is dissolved in water and tested, what happens to litmus?
Metal oxides are basic. When magnesium oxide dissolves it forms an alkali, which turns red litmus blue. Non-metal oxides, by contrast, are acidic.
When magnesium burns, its mass increases. Why?
During burning, oxygen atoms from the air combine with the magnesium to form magnesium oxide. Because extra oxygen is added, the product weighs more than the magnesium ribbon did.
- A metal oxide — correct
- A metal hydroxide
- A metal salt and hydrogen
- Just heat, with no new substance
- It turns red litmus blue, because metal oxides are basic — correct
- It turns blue litmus red, because metal oxides are acidic
- It has no effect on litmus at all
- It bleaches the litmus white
- Because oxygen from the air is added to the magnesium — correct
- Because the magnesium gives off a gas and loses matter
- Because heat has weight that soaks in
- Because the magnesium turns into water