The electrolysis of water involves the decomposition of water (H₂O) into hydrogen gas (H₂) and oxygen gas (O₂) using electrical energy. This is a non-spontaneous reaction, requiring an electrolytic cell.
Reaction:
2H2O(l)→electrolysis→2H2(g)+O2(g)
Process:
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Electrolytic Cell Setup: The cell consists of two electrodes—an anode (positive electrode) and a cathode (negative electrode)—placed in water with an electrolyte (often a dilute acid like sulfuric acid, H₂SO₄, or an alkali like sodium hydroxide, NaOH, to increase water’s conductivity).
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At the Anode (Oxidation): Water molecules lose electrons (oxidation), forming oxygen gas and hydrogen ions (protons):
2H2O→O2+4H++4e−
Oxygen gas (O₂) is produced at the anode.
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At the Cathode (Reduction): Hydrogen ions (H⁺) gain electrons (reduction), forming hydrogen gas:
4H++4e−→2H2
Hydrogen gas (H₂) is produced at the cathode.
Conditions for Electrolysis of Water:
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Voltage: A minimum voltage of 1.23 V is required to break the bonds in water molecules. However, in practice, a higher voltage is often applied due to inefficiencies and losses.
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Electrodes: Platinum or graphite is commonly used as electrodes because they are inert and do not participate in the reaction.
Products: Hydrogen gas is produced at the cathode, and oxygen gas is produced at the anode. The volume of hydrogen produced is twice that of oxygen, following the stoichiometric ratio of 2:1.
Applications:
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Electrolysis of water is used to produce hydrogen gas for fuel cells and other chemical processes.
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It is also a method for obtaining oxygen and hydrogen in pure forms.