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Which ion reduces at the cathode during electrolysis of fresh brine solution?
Cl тБ╗
H +
OH тБ╗
Na +
H +
During the electrolysis of a fresh brine solution (an aqueous solution of sodium chloride, NaCl), water molecules and sodium/chloride ions are present. At the cathode (negative electrode), reduction takes place where hydrogen ions (or water molecules accepting electrons) have a lower discharge potential than sodium ions, leading to the reduction of H+ ions into hydrogen gas (H2).
During the electrolysis of a fresh brine solution (an aqueous solution of sodium chloride, NaCl), water molecules and sodium/chloride ions are present. At the cathode (negative electrode), reduction takes place where hydrogen ions (or water molecules accepting electrons) have a lower discharge potential than sodium ions, leading to the reduction of H+ ions into hydrogen gas (H2).
Industrial Chemistry and Chlor-Alkali Process: The electrolysis of brine in castner-kellner or diaphragm cells is a foundational chemical process used globally to manufacture sodium hydroxide, chlorine gas, and hydrogen gas.
Cathode is the negative electrode where reduction (gain of electrons) takes place.
During brine electrolysis, Na+ and H+ ions migrate towards the cathode.
Due to standard reduction potentials, H+ ions (from water/acid) are discharged in preference to Na+ ions.
Hydrogen gas (H2) is liberated at the cathode, while chlorine gas (Cl2) is liberated at the anode.
Option B (H+) is correct because hydrogen ions have a higher reduction potential than sodium ions.
Option D (Na+) remains in solution along with OH- ions, forming sodium hydroxide (NaOH), which is why this is known as the Chlor-Alkali process.
Option A (Cl-) is oxidized at the anode to release chlorine gas.
Option C (OH-) remains unoxidized at the anode under normal brine concentration conditions as water molecules/chloride ions react preferentially.
B is correct тАФ Hydrogen ions (H+) are reduced at the cathode during the electrolysis of a fresh brine solution.
In general science exam questions on electrochemistry, always remember that cations lower in the reactivity series (like H+, Cu2+, Ag+) are discharged at the cathode before active metal cations (like Na+, K+, Ca2+).
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