In a dilute aqueous sodium chloride (NaCl) solution, electrolysis can occur when an electric current is passed through the solution. During this process, two electrodes are involved: the anode (positive electrode) and the cathode (negative electrode).
At the cathode, reduction occurs. In a dilute NaCl solution, the two possible reduction reactions are:
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The reduction of sodium ions (Na⁺) to form sodium metal: \[ \text{Na}^+ + e^- \rightarrow \text{Na} \]
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The reduction of water to form hydrogen gas (H₂): \[ 2 \text{H}_2\text{O} + 2 e^- \rightarrow \text{H}_2 + 2 \text{OH}^- \]
However, sodium metal is very reactive and the standard reduction potential for sodium ion is much lower than that of water. Thus, in practice, water is reduced instead of sodium ions.
Therefore, the cathode product of dilute aqueous sodium chloride solution is hydrogen gas (H₂).