11.2 - Chemical Effects of Electric Current

The passage of electric current through a conductor can cause various chemical changes. This phenomenon is known as the chemical effects of electric current. These effects are used in many applications, such as electroplating, extraction of metals, and electrolysis. The chemical effects occur because the electric current causes ions in the electrolyte to move and participate in chemical reactions.

When an electric current passes through a conducting solution (electrolyte), it causes the ions in the solution to move towards the electrodes. The positive ions move towards the negative electrode (cathode), and the negative ions move towards the positive electrode (anode). At these electrodes, chemical reactions occur, leading to the formation of new substances.

Electrolysis

Electrolysis is a process in which an electric current is used to drive a non-spontaneous chemical reaction. During electrolysis, the electrolyte (a solution or molten compound) undergoes decomposition. The products formed at the electrodes depend on the type of electrolyte used. For example, when a current passes through water, the water molecules decompose into hydrogen and oxygen gases.

For water electrolysis, the reactions at the electrodes are:

• At the cathode (reduction): $2H_2O + 2e^- \rightarrow H_2 + 2OH^-$
• At the anode (oxidation): $2H_2O \rightarrow O_2 + 4H^+ + 4e^-$

These reactions show that water decomposes into hydrogen gas at the cathode and oxygen gas at the anode.

Electroplating

Electroplating is the process of coating a metal object with a thin layer of another metal using electrolysis. This is widely used for decorative purposes and to prevent corrosion. In electroplating, the object to be plated is made the cathode, and the metal to be plated is made the anode. The electrolyte contains the metal salt, and the metal ions are reduced at the cathode, forming a metallic layer.

The general reaction for electroplating a metal (say, silver) can be represented as:

• At the cathode (reduction): $Ag^+ + e^- \rightarrow Ag$
• At the anode (oxidation): $Ag \rightarrow Ag^+ + e^-$

Here, silver ions from the electrolyte are reduced to form a thin layer of silver on the cathode (the object being plated), while silver metal from the anode dissolves into the solution as silver ions.

Electrolysis of Copper Sulfate Solution

When an electric current passes through a copper sulfate solution, copper metal is deposited at the cathode, and oxygen gas is released at the anode. The reactions at the electrodes are:

• At the cathode (reduction): $Cu^{2+} + 2e^- \rightarrow Cu$
• At the anode (oxidation): $4OH^- \rightarrow O_2 + 2H_2O + 4e^-$

This process is commonly used for the purification of copper, where impure copper is used as the anode and pure copper is deposited at the cathode.

Applications of Chemical Effects of Electric Current

Some common applications of chemical effects of electric current include:

• Electroplating – coating a metal with another metal to prevent corrosion or for decoration.
• Electrorefining – purifying metals like copper.
• Extraction of metals – certain metals can be extracted from their ores using electrolysis.
• Electrolysis in industries – used for producing chemicals such as chlorine and sodium hydroxide.

The chemical effects of electric current have numerous practical applications in various fields such as industry, technology, and daily life.