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How do you purify copper by electrolysis?

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Electrolysis involves using an electrical current between a negatively charged cathode and a positively charged anode to dissolve impure copper in a bath of copper(II) sulphate. An impure-copper casting is attached to the anode, and a piece of pure copper is attached to the cathode. When the electric current is passed through the anode, cathode and copper(II) sulphate, the impure copper dissolves. The purified copper migrates to the cathode, and the impurities deposit at the bottom of the solution.

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Full Answer

The electric current facilitates electrolysis by causing chemical changes to the copper attached to the anode and cathode. The positively charged copper atoms from the impure casting are attracted to the negatively charged pure copper atoms. The anode then begins to oxidize, and the positively charged copper atoms from into blue-copper(II) ions. The cathode's negative charge reduces when the positively charged copper(II) ions build up around the cathode and become neutral copper atoms.

Although the material deposited at the bottom of the copper(II) sulphate solution are impurities, they are not necessarily a waste product. Depending on the content of the copper casting, the by-product of the electrolysis may contain valuable metals, such as silver. While the process works well to remove impurities from copper castings that are harvested from ores, electrolysis can also be used to purify recycled copper. The practice of purifying recycled copper is cheaper than beginning the process with smelted copper due to the scarcity and value of high-grade copper ores.

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