Question

Give reason: Carbonate and sulphide ores are usually converted into oxides during the process of extraction.

Answer 1

Hint: In this question, we just need to think about how a metal (in pure form) can be obtained easily. The conversion of metal oxides to metals is an easier process when compared to conversion of metal carbonate and sulfides to metals.

Complete Solution :
Sulphide ores are converted to oxides by heating in the presence of excess air. This process is known as Roasting. Carbonates are changed into oxides by strongly heating them in limited air. The process is known as Calcination. Carbonate and sulphide ores are usually converted into oxides during the process of extraction because extraction of metal is easier from their oxides rather than from their carbonates or sulphides. As with the case of oxides, we simply have to use a metal more reactive than the impure metal which needs to be extracted.

Note: A reaction involving calcination can be represented as follows:
 When zinc carbonate is heated strongly in the absence of air, it decomposes to form zinc oxide and carbon dioxide.
\[ZnC{{O}_{3}}\left( s \right)\to ZnO\left( s \right)+C{{O}_{2}}\left( g \right)\]

- A reaction involving roasting can be represented as follows:
When zinc sulphide is strongly heated in the presence of air it gets converted to zinc oxide
\[2ZnS\left( s \right)+3{{O}_{2}}\left( g \right)\to 2ZnO\left( s \right)+2S{{O}_{2}}\left( g \right)\]

Now, we have obtained zinc (oxide of the desired metal) in both the cases. Since, we know that carbon is more reactive than metals like zinc. Hence, this zinc oxide is heated with carbon. This results in Carbon displacing zinc to form carbon monoxide and yielding zinc metal.
\[ZnO\left( s \right)+C\left( s \right)\to Zn\left( s \right)+CO\left( g \right)\]