Electrolysis of Water

Electrolysis of water is a fundamental chemical process used to decompose water (H₂O) into its constituent gases, hydrogen (H₂) and oxygen (O₂), by passing an electric current through it. This process requires an electrolyte to increase the conductivity of pure water, which is otherwise a poor conductor of electricity. Common electrolytes like salt (NaCl), dilute sulphuric acid (H₂SO₄), or sodium hydroxide (NaOH) are added for effective electrolysis.

• The process takes place in an electrolytic cell where two electrodes (cathode and anode) are submerged in an electrolyte solution.
• When a direct current (DC) is applied, water molecules dissociate: hydrogen gas is released at the cathode (negative electrode), and oxygen gas is released at the anode (positive electrode).
• The volume of hydrogen gas formed is approximately twice that of oxygen, consistent with the molecular composition of water (H₂O).
• Electrolysis of water is not only a practical demonstration of water's composition but also a significant industrial process.
• It is widely used for producing hydrogen gas, which serves as a clean energy carrier and is critical for applications like fuel cells, ammonia production, and refining metals. 

1. Aim: To demonstrate the electrolysis of water and observe the formation of hydrogen and oxygen gases at the cathode and anode, respectively.

2. Requirements: 500 ml of pure water, 2 g of salt, a beaker (500 ml capacity), test tubes (2), electrical wires with cladding removed (2 cm at the ends), DC power supply (6V potential difference), litmus paper, and optional electrolytes: dilute H₂SO₄ and dilute NaOH.

3. Procedure

• Dissolve 2 g of salt in 500 ml of pure water and take 250 ml of the solution in a beaker.
• Connect two wires to the terminals of a 6V power supply and immerse their exposed ends as electrodes in the solution.
• Fill two test tubes with the solution and invert them over the electrodes without trapping air.
• Turn on the power supply, allowing current to pass through, and observe gas bubbles forming in the test tubes.
• Note the difference in gas volumes; test the solutions with litmus paper to identify acidity and alkalinity.
• Repeat using dilute H₂SO₄ and dilute NaOH as electrolytes and record observations.

Electrolysis of water

4. Observations: Gas bubbles form near both electrodes. The volume of gas collected at the cathode is approximately double that of the gas collected at the anode. Testing with litmus paper shows the solution near the cathode is basic (turns blue) and near the anode is acidic (turns red).

5. Conclusion: The experiment shows the electrolysis of water-

• Hydrogen gas forms at the cathode (2H₂O + 2e⁻ → H₂ + 2OH⁻).
• Oxygen gas forms at the anode (2H₂O → O₂ + 4H⁺ + 4e⁻).

The volume ratio of hydrogen to oxygen is 2:1, confirming the composition of water (H₂O). Using dilute H₂SO₄ or NaOH enhances conductivity and results in similar observations.