When copper is purified from copper sulfide, copper is reduced

to its metallic form through a process known as smelting. The copper sulfide ore is first crushed and ground to a fine powder. It is then mixed with carbon and heated in a furnace to high temperatures, causing the sulfur in the ore to react with the carbon and form carbon dioxide gas. This leaves behind pure copper metal, which can then be further processed and purified as needed. The process of reduction involves the transfer of electrons from the carbon to the copper ions in the sulfide ore, converting them into pure copper metal.