Chemistry Electrochemistry MDCAT 2017
PMDC Verified Question 60 of 73
The E° value of standard copper half-cell is +0.34V, measured when it is connected with SHE i.e. Standard hydrogen electrode. In this case the half reaction taking place at SHE is:
A
\( 2H^+_{(aq)} + 2e^- \rightarrow H_{2(g)} \)
B
\( H_{2(g)} \rightarrow 2H^+_{(aq)} + 2e^- \)
C
\( 2H^+_{(aq)} + 2e^- \rightarrow 2H_{2(g)} \)
D
\( H_{2(g)} \rightarrow 2H_{(g)} + 2e^- \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( H_{2(g)} \rightarrow 2H^+_{(aq)} + 2e^- \)
Concept:

When two half-cells are connected, the one with the higher (more positive) standard reduction potential acts as the cathode (undergoes reduction), and the other acts as the anode (undergoes oxidation).

Solution:

  • Copper has a standard reduction potential of \( +0.34 \text{ V} \), which is greater than that of SHE (\( 0.00 \text{ V} \)).


  • Because Copper has a higher reduction potential, it forces the SHE to act as the anode.


  • At the anode, oxidation (loss of electrons) occurs.


  • The oxidation half-reaction for hydrogen gas is: \( H_{2(g)} \rightarrow 2H^+_{(aq)} + 2e^- \).


Why other options are incorrect:

Option A represents reduction, which would only happen if SHE were connected to a metal with a negative reduction potential (like Zn). Option C is stoichiometrically incorrect. Option D shows the formation of atomic hydrogen gas instead of aqueous \( H^+ \) ions.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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