Explain why aluminium cannot be extracted from aluminium oxide by heating with carb...
Check the final answer first, then review the worked steps.
Problem
Explain why aluminium cannot be extracted from aluminium oxide by heating with carbon, given that lead can be extracted from lead oxide by heating with carbon.
Answer
Aluminium is more reactive than carbon, so carbon cannot displace it from aluminium oxide. Lead is less reactive than carbon, so carbon can displace it from lead oxide.
Step-by-step solution
1. Understand Reactivity Series: The ability of carbon to reduce metal oxides depends on the reactivity of the metal. Metals higher in the reactivity series are more difficult to reduce. The reactivity series ranks metals based on their tendency to lose electrons and form positive ions. A simplified reactivity series from most reactive to least reactive is: Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Lead, Copper, Silver, Gold.
2. Compare Reactivity of Aluminium and Lead: Aluminium is significantly more reactive than lead. This means that aluminium has a stronger attraction to oxygen than lead does.
3. Explain Carbon's Reducing Power: Carbon is a reducing agent, meaning it can remove oxygen from metal oxides. However, carbon can only effectively reduce metal oxides of metals that are less reactive than carbon itself. In the reactivity series, lead is below carbon, while aluminium is above carbon.
4. Conclusion for Aluminium Extraction: Because aluminium is more reactive than carbon, carbon cannot displace aluminium from aluminium oxide ($Al_2O_3$). The bond between aluminium and oxygen is too strong to be broken by carbon alone. Therefore, a different method, such as electrolysis, is required to extract aluminium from its ore.
5. Conclusion for Lead Extraction: Since lead is less reactive than carbon, carbon can readily displace lead from lead oxide ($PbO$) when heated, forming molten lead and carbon dioxide ($CO_2$). The reaction is $2PbO(s) + C(s)
ightarrow 2Pb(l) + CO_2(g)$.