Electrolysis is a chemical process that uses an electric current to drive a non-spontaneous reaction. It occurs in an electrolytic cell, where two electrodes, the anode (positive electrode) and cathode (negative electrode), are immersed in an electrolyte solution. The activities at the cathode and anode during electrolysis depend on the electrolyte used and the substances present in the solution.
Activities at the Cathode (Negative Electrode)
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Reduction Reaction: At the cathode, reduction occurs, meaning that cations (positive ions) gain electrons. This can lead to various reactions depending on the ions in the solution.
- For example:
- In an aqueous solution of copper(II) sulfate (CuSO₄), copper ions (\(Cu^{2+}\)) are reduced to solid copper: \[ Cu^{2+} + 2e^- \rightarrow Cu(s) \]
- In a solution containing hydrogen ions (like dilute sulfuric acid, H₂SO₄), water can be reduced to produce hydrogen gas: \[ 2H^+ + 2e^- \rightarrow H_2(g) \]
- For example:
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Gas Evolution: If the cathode reaction produces a gas, the gas will bubble up and can be collected (e.g., H₂ gas from water during the electrolysis of water).
Activities at the Anode (Positive Electrode)
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Oxidation Reaction: At the anode, oxidation occurs, meaning that anions (negative ions) lose electrons. This process can also vary based on the ions present in the solution.
- For instance:
- In the case of the electrolysis of water, hydroxide ions (\(OH^-\)) can be oxidized to produce oxygen gas: \[ 4OH^- \rightarrow O_2(g) + 2H_2O + 4e^- \]
- In an aqueous solution of CuSO₄, if no other ions are competing, sulfate ions may remain in solution, while water might oxidize: \[ 2H_2O \rightarrow O_2(g) + 4H^+ + 4e^- \]
- For instance:
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Gas Evolution: Similar to the cathode, if the anode reaction produces a gas (like oxygen), it will also bubble and can be collected during electrolysis.
Summary
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Cathode Reactions:
- Cations gain electrons (reduction).
- It often results in the deposition of a metal or the evolution of gas (like H₂).
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Anode Reactions:
- Anions lose electrons (oxidation).
- It often leads to the evolution of gas (like O₂) or the oxidation of anions.
The specific reactions at each electrode depend on the substances present in the electrolyte, the nature of the electrodes, the concentration of the ions, and the applied voltage.