Electrolysis is the chemical decomposition of an electrolyte when an electric current is passed through it.

Electrolysis is a process where an electric current is passed through an electrolyte (a substance that conducts electricity), causing a chemical reaction that splits the substance into its constituent elements or compounds. This process is widely used in various applications, including metal extraction, water purification, and the production of chemicals like chlorine and hydrogen gas.

1. Electrolysis: The process in which an electric current causes a chemical change in an electrolyte, resulting in the decomposition of the substance.

2. Electrolyte: A substance (molten or in aqueous solution) that conducts electricity and decomposes during electrolysis.

3. Anode : The anode is the electrode where electrons flow out of the electrolyte, making it the positive terminal. Oxidation occurs here, releasing electrons into the external circuit. It's the site where negatively charged ions (anions) are attracted and give up electrons, becoming neutral or positively charged.

4. Cathode: The cathode is the electrode where electrons flow into the electrolyte, making it the negative terminal. Reduction occurs here, gaining electrons from the external circuit. It's the site where positively charged ions (cations) are attracted and receive electrons, becoming neutral or negatively charged.

5. Current Flow: Conventional current flows from the anode (positive) to the cathode (negative) , while electrons flow in the opposite direction, from anode to cathode.

6. Electrolytic Cell: A setup in which electrical energy is used to carry out electrolysis using electrodes dipped in an electrolyte.

The Ionic Theory, proposed by S. Arrhenius, states that when an electrolyte is dissolved in water, it splits (dissociates) into freely moving charged particles called ions. These ions are responsible for conducting electricity in solution.

Strong electrolytes dissociate completely into ions while weak electrolytes dissociate partially. The movement of positive ions (cations) towards the cathode and negative ions (anions) towards the anode explains why electrolyte solutions conduct electricity.

Example of Ionic Dissociation Reaction

Sodium chloride in water:
$$\text{NaCl}_{(aq)} \rightarrow \text{Na}^+_{(aq)} + \text{Cl}^-_{(aq)}$$

Sulphuric acid in water:
$$\text{H}_2\text{SO}_4 \rightarrow 2\text{H}^+ + \text{SO}_4^{2-}$$

These ions carry electric current when a potential difference is applied.

This experiment shows that electrolytes conduct electricity because they contain ions, while non-electrolytes do not.

Apparatus

• Filter paper
• Two carbon electrodes
• DC power supply or 9V battery
• Solutions: salt solution, sugar solution, tap water
• Universal indicator or phenolphthalein

Procedure

1. Soak a strip of filter paper in the solution to be tested (e.g., salt solution).
2. Place the wet filter paper on a non-metallic surface.
3. Touch the two electrodes at the ends of the filter paper.
4. Add a few drops of indicator to the paper.

Observation

In salt solution, the area around one electrode turns red/pink (acidic) while the area around the other turns blue/purple (alkaline). This colour change shows ions moving and reacting at the electrodes.

Chemical Reactions

At the cathode (reduction): $$\text{H}_2\text{O} + e^- \rightarrow \text{OH}^- + \tfrac{1}{2}\text{H}_2$$

At the anode (oxidation): $$\text{Cl}^- \rightarrow \tfrac{1}{2}\text{Cl}_2 + e^-$$

The formation of H₂, Cl₂, and OH^- ions proves electrical conduction and therefore supports the ionic theory.

Conclusion

The filter paper changes colour only when ions are present. Sugar solution and distilled water show no colour change, proving they do not contain ions and cannot conduct electricity.

Conductors are substances that allow electricity to pass through them. Metallic conductors transmit electricity by the movement of electrons and do not undergo chemical decomposition.

A conductor is a material that allows the flow of electric charge — e.g., metals (electrons move). An electrolyte is a substance (usually ionic) that conducts when molten or in solution because charged ions move. In metals charge is carried by electrons; in electrolytes charge is carried by ions.

Strong Electrolytes: Completely ionize in water (e.g. HCl, NaCl, KOH).

Weak Electrolytes: Partially ionize in water (e.g. CH₃COOH, NH₄OH).