Question

Describe how impure copper obtained from the smelting of ore is purified by electrolysis

Short answer

Impure copper obtained from the smelting of ore is purified through electrolysis with a setup involving an impure copper anode, a pure copper cathode, and a copper sulfate electrolyte. During electrolysis, the impure copper anode dissolves into the electrolyte as copper ions by the oxidation reaction \(Cu \rightarrow Cu^{2+} + 2e^-\). Simultaneously, copper ions in the electrolyte are reduced at the cathode, depositing pure copper by the reaction \(Cu^{2+} + 2e^- \rightarrow Cu\). The impurities remain either on the anode or fall as sludge. The result is the purification and transfer of copper from the anode to the cathode.

Step-by-step solution

Understanding Electrolysis

Electrolysis is a process in which electrical energy, supplied by a direct current (DC), is used to drive a non-spontaneous chemical reaction. In the case of copper purification, we use electrolysis to separate impure copper from its impurities, obtaining pure copper at the end of the process.

Setting Up the Electrolysis Apparatus

The electrolysis of copper is set up with two electrodes immersed in a suitable electrolyte. The impure copper, which needs to be purified, is used as the anode, and a thin sheet of pure copper is used as the cathode. Both electrodes are connected to an external power source, with the anode connected to the positive terminal and the cathode connected to the negative terminal. The electrolyte, typically a copper sulfate solution, contains copper ions that will help drive the electrolysis process.

Reactions at the Anode

When the current is turned on, oxidation occurs at the anode. The impure copper loses electrons and dissolves into the electrolyte, releasing copper ions. The reaction at the anode is: \(Cu \rightarrow Cu^{2+} + 2e^-\) The impurities in the copper do not dissolve in the electrolyte and either drop to the bottom of the cell as sludge or remain as an insoluble layer on the anode.

Reactions at the Cathode

At the cathode, the copper ions in the electrolyte are reduced and gain electrons, forming pure copper atoms that are deposited onto the cathode. The reaction at the cathode is: \(Cu^{2+} + 2e^- \rightarrow Cu\)

Purification of Copper

As the electrolysis process continues, the impure copper anode dissolves into the electrolyte and pure copper is deposited onto the cathode. This process transfers the copper from the anode to the cathode, making the cathode gradually thicker while the anode becomes thinner. The impurities in the anode either fall to the bottom of the cell as sludge or remain at the anode. After the electrolysis is complete, the pure copper cathode can be removed and used, while the polluting impurities can be recovered from the sludge or insoluble layer. This summarizes the process of purifying impure copper obtained from the smelting of ore through electrolysis, focusing on the electrolysis setup, the reactions taking place at both the anode and cathode, and the transfer of copper, leaving impurities behind.

Key concepts

Electrolysis

Electrolysis is a key chemical process used to purify metals, such as copper, by means of electrical energy. This fascinating technique requires an external voltage source that initiates and maintains a flow of electrical current through a liquid medium. As electricity is applied, ions within the solution undergo chemical transformations at specific locations called electrodes. In the context of copper purification, electrolysis is particularly effective. This is because imbalances in charges facilitate the separation of copper atoms from impurities. Through this method, one achieves not only metal purification but also greater control of the reaction process.
By employing electrolysis, impurities can be left behind, as only pure copper ions are selectively deposited onto the designated surface.

Anode and Cathode Reactions

Fundamental to the electrolysis of copper are the reactions that happen at the electrodes—the anode and cathode. Initially, the impure copper serves as the anode, a positive electrode where oxidation occurs. At this point, copper atoms release electrons, transforming into copper ions with the equation: \[Cu \rightarrow Cu^{2+} + 2e^-\] As these positive copper ions dissolve into the electrolyte, they journey toward the cathode.
At the cathode, a negative electrode, a reduction reaction happens. Here, the copper ions gain electrons, converting back into solid copper atoms with the equation:
\[Cu^{2+} + 2e^- \rightarrow Cu\] These newly formed copper atoms are then deposited onto the cathode, gradually building up pure copper in its solid form. These crucial reactions define the essence of copper purification by electrolysis.

Impurities in Copper

While electrolysis effectively purifies copper, the process also highlights the importance of managing impurities. Initially intermingled with the copper in the anode, these impurities do not dissolve into the solution during the electrochemical reactions.
Instead, they remain behind in various forms:

• Some impurities fall to the bottom of the electrolytic cell as sludge.
• Others create an insoluble layer on the surface of the anode.

The management of these impurities is crucial. Not only can they be contaminants, but they also often contain valuable metals such as gold and silver. These can be carefully collected and reused, contributing to the economic efficiency of the electrolysis process.

Copper Sulfate Electrolyte

Central to the process of copper purification is the copper sulfate electrolyte. This solution acts as the medium facilitating the flow of copper ions between the anode and cathode. Copper sulfate, with the chemical formula \(CuSO_4\), is dissolved in water to create this electrolyte. Its significance is due to the presence of copper ions, which are essential for driving the electrolysis process.
Additionally, the sulfate ions in the solution help balance the charge as the reactions take place at the electrodes. After connecting the apparatus, this electrolyte enables continuous ion exchange, crucial for the efficient transfer and deposition of pure copper. The role of copper sulfate as an electrolyte can thus not be overstated—it is integral to achieving a seamless and effective purification process.