9701 · 24.1
Electrolysis
Electrolysis uses a direct current power supply to force a non-spontaneous redox reaction to occur. This process is fundamental to splitting compounds and producing elements like chlorine and aluminium.
Need to know
What you need to know
- **Cathode:** The negative electrode. It is connected to the negative terminal of the power supply. Positive ions (cations) migrate here and are reduced (gain electrons).
- **Anode:** The positive electrode. It is connected to the positive terminal of the power supply. Negative ions (anions) migrate here and are oxidised (lose electrons).
- **Electron Flow:** Electrons flow from the anode, through the external circuit to the power supply, and from the power supply to the cathode. The ions carry the charge within the electrolyte itself.
Explanation
Forcing Reactions with Electricity
- Electrolysis uses a direct current (DC) power supply to drive a non-spontaneous redox reaction at electrodes within an electrolyte.
- Positive cations move to the negative cathode for reduction (gain of electrons), while negative anions move to the positive anode for oxidation (loss of electrons).
- In molten electrolytes, only the compound's ions react. In aqueous solutions, water can also be oxidised (to O₂) or reduced (to H₂), so H⁺ and OH⁻ ions compete with the solute ions at the electrodes.
- Faraday's laws state that the mass of product is proportional to the total electric charge passed. We use Q = It and n = Q/F to calculate the moles of product formed.