The Basics of Electrolysis

Electrolysis is a process that involves using an electrical current to trigger the decomposition (breaking down) of ionic compounds into simpler substances. To understand electrolysis, it is important to understand the components involved in the process:

  • Electrolyte – A substance that can conduct electricity when it is either molten or dissolved in a solution. The electrolyte is the substance which gets decomposed during electrolysis.
  • Electrode – A conductor of electricity that is usually a metal or graphite rod. It is connected to the power supply and can be either an anode or a cathode.
  • Anode – The positive electrode that is connected to the positive terminal of a battery.
  • Cathode – The negative electrode that is connected to the negative terminal of a battery.

Electricity is the flow of charged particles. We usually think of electricity occurring through metal wires. However, some liquids can also transfer electricity, behaving like wires, due to the presence of ions (charged particles) that carry the charge.

Movement of Electrons

Electrolysis involves the movement of electrons (negatively charged particles), which is driven by an electrical current. Here’s how it works:

1. The cathode is negatively charged, which attracts positively charged cations. At the cathode, the cations are reduced, which means they gain electrons.

2. The anode is positively charged, which attracts negatively charged anions. At the anode, the anions are oxidised, which means they lose electrons.

For example, if molten sodium chloride is subjected to electrolysis, the positively charged sodium ions (Na+) are attracted to the cathode, where they gain electrons. Meanwhile, the negatively charged chloride ions (Cl) are attracted to the anode, where they lose electrons.

Electrolysis apparatus showing the power supply, anode, and cathode. Chloride ions are at the anode and sodium ions at the cathode.

  • During electrolysis, both the anode and the cathode are connected to the power supply

Remember that opposites attract, so the anode is positive and the cathode is negative. However, if you’re struggling to remember which one is positive and which is negative, remember not to PANIC: Positive (is) Anode, Negative Is Cathode.

Products of Electrolysis

When an electrolysis reaction occurs, the electrolyte solution or liquid is broken down into its chemical components. For example, if molten lead chloride is subjected to electrolysis, it will be broken down to form both lead and chlorine.

Electrolytes

Electrolytes are substances that can conduct an electrical charge due to the presence of ions. To be an electrolyte, a substance must be able to conduct electricity.

Covalent compounds can not be electrolytes

Covalently bonded compounds cannot be electrolytes as they can’t carry the electrical charge through the solution. Therefore, they can’t undergo electrolysis.

For example, ethanol is a covalent compound and therefore is not an electrolyte, whereas sodium chloride is an ionic compound and can be an electrolyte.

On the left: An electrolysis apparatus without current, showing an unlit bulb and no ion movement. On the right: An apparatus with current, indicating ion movement and a lit bulb.

But remember that ionic compounds cannot conduct electricity in a solid state, as there are no free ions to move and carry the charge. So, the ionic compound must be in a molten state or dissolved in a solution to conduct electricity.

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