Animated Solution for Chemistry - Metallurgy: Upon heating with ${\text{Cu}}_2\text{S}$, the reagent(s) that give copper metal is/are

In the fascinating world of metallurgy, extracting a pure metal from its raw ore is like solving a complex chemical puzzle. When it comes to copper, nature provides us with ores like copper pyrites (${\text{CuFeS}}_2$) and copper glance (${\text{Cu}}_2\text{S}$). The journey from a rocky sulfide to shiny, pure copper involves several ingenious steps, but none is more elegant than the final reduction phase.

Typically, to extract a metal from its oxide, we use a reducing agent like carbon (coke) or carbon monoxide. This is standard practice in the extraction of iron. However, copper has a trick up its sleeve. Using carbon for copper extraction isn't always the most efficient or economical route, especially when dealing with sulfide ores. Instead, metallurgists rely on a process that feels almost like the ore is doing the work for us.

Before we can get pure copper, the concentrated ore is heated in the presence of excess air in a reverberatory furnace. This process is called roasting. During roasting, a portion of the copper(I) sulfide (${\text{Cu}}_2\text{S}$) reacts with oxygen to form copper(I) oxide (${\text{Cu}}_2\text{O}$) and sulfur dioxide gas.

This step is crucial because it sets the stage for the grand finale. We don't want to oxidize all the sulfide; we intentionally leave some of it unreacted.

Here is where the magic happens. The mixture is transferred to a Bessemer converter. As the temperature rises, the newly formed copper(I) oxide (${\text{Cu}}_2\text{O}$) comes into contact with the remaining unreacted copper(I) sulfide (${\text{Cu}}_2\text{S}$).

Instead of adding an external reducing agent, the sulfide itself acts as the reducing agent for the oxide! This phenomenon is known as self-reduction or auto-reduction. The sulfur in the sulfide grabs the oxygen from the oxide, forming sulfur dioxide gas, and leaving behind pure copper metal.

The Final Product

As the reaction proceeds, the molten copper begins to cool and solidify. The sulfur dioxide gas produced in the reaction bubbles out of the molten mass. As these gas bubbles escape, they leave behind blister-like marks on the surface of the solidifying metal. Because of this unique appearance, the resulting metal is affectionately called blister copper, which is about 98% pure.

So, when asked what reagent gives copper metal upon heating with ${\text{Cu}}_2\text{S}$, the answer is beautifully simple: its own oxidized counterpart, ${\text{Cu}}_2\text{O}$.