What product is obtained at the cathode during the electrolysis of concentrated aqueous sodium chloride (brine) in a diaphragm or membrane cell?
Answer and explanation
Correct answer: D. Hydrogen gas (H2)
- Step 1: In aqueous brine, both Na+ and H+ (from H2O) are present at the cathode. Step 2. The reduction potential of H+ (2 H2O + 2 e- -> H2 + 2 OH-, E° = -0.83 V) is far more favorable than reduction of Na+ (E° = -2.71 V). Step 3. Therefore, H2 gas is evolved at the cathode while Cl2 gas evolves at the anode. Answer: Hydrogen gas (H2). Why not the others: Sodium metal is produced only in molten NaCl (Downs cell); chlorine evolves at the anode.
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