Apentix/AP Chemistry/Unit 9: Applications of Thermodynamics/Question

AP Chemistrymediummcq1 pt

When aqueous NaCl is electrolyzed instead of molten NaCl, what forms at the cathode, and why?

A.H₂ gas, because water is reduced more easily than Na⁺

B.Na metal, just as in molten-salt electrolysis

C.O₂ gas, because water is oxidized at the cathode

D.Solid NaOH, which plates onto the electrode surface

Explanation

Core Concept

Two reducible species compete at the cathode: Na⁺ with E° = −2.71 V and water near −0.83 V for hydrogen evolution in neutral solution. Water's far less negative potential lets it accept electrons preferentially, so H₂ bubbles off and sodium metal never appears. Na⁺ stays dissolved beside the OH⁻ generated at the electrode; only molten salt, lacking water, yields collectible sodium.

Correct Answer

AH₂ gas, because water is reduced more easily than Na⁺

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