Electrolysis is the use of an electric current to bring about a chemical reaction.

Example: Electrolysis of copper (II) sulfate solution with active copper electrodes

Procedure

• Set up the apparatus as shown with two copper rods dipping into copper (II) sulfate solution.
• One copper rod is the cathode or negative electrode, and the other copper rod is the anode or positive electrode.
• The electrodes here are called active electrodes as they react with the electrolyte.
• Cathode reaction (negative electrode)

It is important to note that reduction occurs at the cathode as it is a negative electrode and donates electrons. (Red Cat)

Copper (II) ions from the solution received two electrons at the cathode and solid copper plates out on the cathode.

Anode reaction (positive electrode):

• Here copper atoms at the anode lose 2 electrons and enter the solution as copper ion.
• Oxidation occurs at the anode.
• The overall result of this electrolysis is the copper anode slowly dissolves in the solution and pure copper is deposited on the cathode.
• This electrolysis is used in industry to purify copper.

Example: Electrolysis of acidulated water using inert platinum electrodes

Procedure:

• In this electrolysis inert platinum electrodes are used. The word inert signifies that the electrodes are not reactive and do not get involved in the electrolysis.
• A Hoffman Voltameter apparatus is used to pass an electric current through water to which some dilution of sulfuric acid has been added.
• Hydrogen gas is produced at the cathode and oxygen is produced at the anode.

Cathode reaction (reduction):

Hydrogen ions in the solution receive 2 electrons and produce hydrogen gas at the cathode.

Anode reaction (oxidation):

Water molecules break down at the anode, producing oxygen gas.

The overall reaction is the breakdown of water into hydrogen and oxygen.

It is important to note that there is twice as much hydrogen produced as oxygen and this proves that the correct formula of water is H2O.

Example: Electrolysis of Aqueous Sodium Sulfate with Universal Indicator

When sodium sulfate dissolves in water, it dissociates into sodium ions ($Na^+$) and sulfate ions ($SO_4\ ^{2-}$). In the electrolysis of sodium sulfate using inert electrodes (such as platinum), the products at the electrodes are influenced by the water present.

At the Cathode (negative electrode):

Water is reduced to hydrogen gas and hydroxide ions.

The universal indicator turns blue around the cathode due to the production of hydroxide ions (making the solution basic).

At the Anode (positive electrode):

Water is oxidised to oxygen gas and hydrogen ions.

The universal indicator turns red around the anode due to the production of hydrogen ions (making the solution acidic).

Example: Electrolysis of Aqueous Potassium Iodide using inert electrodes and Phenolphthalein Indicator

In the electrolysis of potassium iodide solution using inert electrodes, the key ions involved are potassium ions ($K^+$) and iodide ions ($I^-$).

At the Cathode (negative electrode):

Water is reduced to hydrogen gas and hydroxide ions, similar to the sodium sulfate electrolysis.

The phenolphthalein indicator turns pink around the cathode due to the formation of hydroxide ions (indicating a basic solution).

At the Anode (positive electrode):

Iodide ions ($I^-$) are oxidised to iodine.

The iodine formed at the anode can be observed as a brown colour around the electrode.

Electroplating is a process where electrolysis is used to put a layer of one metal on another.

Example: Electroplating a Nickel Spoon with Silver

Procedure:

Set up the apparatus: Connect the nickel spoon (to be plated) to the negative terminal (cathode) and the silver anode to the positive terminal of the power supply. Submerge both electrodes in a solution of silver nitrate (the electrolyte).

Pass an electric current through the solution to initiate the electroplating process.

Cathode Reaction:

Silver ions ( $\text{Ag}^+$ ) in the solution gain electrons at the cathode (nickel spoon), forming silver metal that plates onto the spoon.

Anode Reaction:

The anode (silver) loses electrons and dissolves into the solution as silver ions ( $\text{Ag}^+$).

Electroplating Process:

As the silver ions are reduced and deposited on the nickel spoon at the cathode, the silver anode dissolves, maintaining a steady concentration of silver ions in the solution. This allows for continuous plating until the desired coating is achieved.

Conditions Needed for Electroplating:

• The object to be plated (nickel spoon) must be connected to the cathode (negative electrode).
• The electrolyte must contain ions of the metal being plated (in this case, silver nitrate).
• The anode must be made of the same metal that is being deposited (silver).