In the electrolysis of water, the decomposition of water into hydrogen and oxygen gases occurs at different rates at the electrodes. This results in differing volumes of gas collected.
Understanding Electrolysis of Water
During electrolysis, water (H₂O) is split into its constituent elements through an electric current. The reaction can be summarized as:
- 2H₂O(l) → 2H₂(g) + O₂(g)
This means that for every two molecules of water, two molecules of hydrogen gas and one molecule of oxygen gas are produced.
Gas Collection at Electrodes
In an electrolysis setup:
- The anode (positive electrode) produces oxygen gas.
- The cathode (negative electrode) produces hydrogen gas.
Given the reaction, the following volumes are generated:
- Hydrogen: 2 molecules produced for every 2 molecules of water.
- Oxygen: 1 molecule produced for every 2 molecules of water.
Volume Ratio Explanation
This results in the following volume relationship:
- For every 2 volumes of hydrogen collected at the cathode, only 1 volume of oxygen is collected at the anode.
Hence, the volume of gas collected at the cathode (hydrogen) is twice that of the gas collected at the anode (oxygen):
- Volume of Hydrogen = 2 × Volume of Oxygen
Conclusion
The fundamental reason for this 2:1 volume ratio in the electrolysis of water stems from the stoichiometry of the chemical reaction involved. Understanding these principles allows students to grasp the concepts of gas production in electrolysis effectively.