The electrochemical cells \(Zn|Zn^{2+}||Cu^{2+}|Cu\) and \(Fe|Fe^{2+}||Cu^{2+}|Cu\) are connected in series. What will be the net emf of the cell at \(27^oC\)?
Given:
\(E^o \text{ of }Zn^{2+}|Zn = - 0.76 V\)
\(E^o \text{ of }Cu^{2+}|Cu = + 0.34 V\)
\(E^o \text{ of }Fe^{2+}|Fe = - 0.41 V\)
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → + 1.85 V
When cells are connected in series, their emfs add up.
Cell 1, Zn|\( \ce{Zn^{2+}} \)||\( \ce{Cu^{2+}} \)|Cu: E°cell = E°right − E°left = 0.34 − (−0.76) = 1.10 V
Cell 2, Fe|\( \ce{Fe^{2+}} \)||\( \ce{Cu^{2+}} \)|Cu: E°cell = 0.34 − (−0.41) = 0.75 V
Net emf = 1.10 + 0.75 = +1.85 V
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | – | – | 02-06 S3 31-05 S1 | – |