If one of the following oxides is heated with hydrogen or carbon using a bunsen burner. it is not reduced to the metal, Which one is it?

Analysis

The question asks which of the listed metal oxides cannot be reduced to its metal form when heated with common reducing agents like hydrogen ($H_2$) or carbon ($C$). This is a test of your knowledge of the Reactivity Series of Metals.

Concept: The Reactivity Series

In chemistry, the ability of a metal oxide to be reduced by carbon or hydrogen depends on the position of the metal in the reactivity series:

1. Low/Moderate Reactivity: Metals like Copper, Lead, and Tin are relatively low in the reactivity series. Their oxides are easily reduced by carbon or hydrogen because the carbon or hydrogen has a higher affinity for oxygen than these metals do.
2. High Reactivity: Metals like Potassium, Sodium, Calcium, and Magnesium are very high in the reactivity series. They have a very strong affinity for oxygen. Because they form very stable oxides, carbon and hydrogen are not strong enough reducing agents to "pull" the oxygen away from them.

Step-by-Step Solution

• Copper oxide ($CuO$): Copper is low in the reactivity series. It is easily reduced by hydrogen: $CuO + H_2 \rightarrow Cu + H_2O$.
• Lead oxide ($PbO$): Lead is moderately reactive. It can be reduced by carbon: $PbO + C \rightarrow Pb + CO$.
• Tin oxide ($SnO_2$): Tin is also moderately reactive and can be reduced by carbon or hydrogen.
• Magnesium oxide ($MgO$): Magnesium is very high in the reactivity series (it is an alkaline earth metal). Its bond with oxygen is extremely strong. Heating $MgO$ with carbon or hydrogen will not result in the formation of magnesium metal because magnesium's affinity for oxygen is much greater than that of carbon or hydrogen.

Conclusion

Since Magnesium is a highly reactive metal, its oxide is stable and cannot be reduced by simple heating with carbon or hydrogen in a laboratory setting.

Exam Tip

Remember the mnemonic for the reactivity series: "Please Stop Calling Me A Careless Zebra Instead Try Learning How Copper Saves Gold." (Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Tin, Lead, Hydrogen, Copper, Silver, Gold). Any metal above Carbon/Hydrogen in this list generally cannot be reduced by them!