The positive value of \(E^\circ_{Cu^{2+}/Cu}\) indicates that
A. copper electrode is a stronger reducing agent than SHE.
B. copper electrode is a stronger oxidising agent than SHE.
C. copper can displace \(H_2\) from \(HCl(aq)\).
D. copper cannot displace \(H_2\) from \(HCl (aq)\).
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → B and D only
Standard electrode potentials are measured against the standard hydrogen electrode (SHE, E° = 0). A positive E° for a couple Mn+/M means that Mn+ is reduced more easily than \( \ce{H^{+}} \): the couple is a weaker reducing agent (and a stronger oxidising agent) than the \( \ce{H^{+}} \)/\( \ce{H2} \) couple. For copper, E°(\( \ce{Cu^{2+}} \)/Cu) = +0.34 V.
To see whether copper can liberate hydrogen from HCl, take the reaction and its cell potential:
\( \ce{Cu(s) + 2H^+(aq) -> Cu^2+(aq) + H2(g)} \)
\( E^\circ_{cell} = E^\circ_{\ce{H+}/\ce{H2}} - E^\circ_{\ce{Cu^2+}/\ce{Cu}} = 0 - 0.34 = -0.34\,\mathrm{V} \)
A negative E°cell means ΔG° is positive, so the reaction does not take place.
(A) copper electrode is a stronger reducing agent than SHE. — Incorrect. A positive E° means copper is a weaker reducing agent than hydrogen.
(B) copper electrode is a stronger oxidising agent than SHE. — Correct. \( \ce{Cu^{2+}} \) takes electrons more readily than \( \ce{H^{+}} \), so the \( \ce{Cu^{2+}} \)/Cu couple is the stronger oxidising agent.
(C) copper can displace \( \ce{H2} \) from HCl(aq). — Incorrect. E°cell for this reaction is −0.34 V, so it is not spontaneous.
(D) copper cannot displace \( \ce{H2} \) from HCl (aq). — Correct. Copper does not dissolve in non-oxidising acids such as HCl; only oxidising acids (nitric acid, hot concentrated sulphuric acid) react with it.
NCERT (2026-27 edition):
Measurement of Electrode Potential – “… 1. A negative E° means that the redox couple is a stronger reducing agent than the H+/H2 couple. 2. A positive E° means that the redox couple is a weaker reducing agent than the H+/H2 couple.”