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Standard electrode potential; Daniell cell EMF

Short answer

Standard electrode potential is the potential of an electrode in 1 M ion solution at 25°C measured against the standard hydrogen electrode. The Daniell cell EMF is calculated using the Nernst equation: E = 1.2 − (0.0591/2) log(0.001/0.1) ≈ 1.26 V.

What is meant by standard electrode potential? Calculate the EMF of a Daniel cell at 25°C, when the concentration of ZnSO₄ and CuSO₄ are 0.001 M and 0.1 M respectively. The standard potential of the cell is 1.2 V.

Standard electrode potential

The electrode potential measured when the electrode is in contact with a 1 M solution of its ions (1 atm for gases) at 25°C, relative to the standard hydrogen electrode (E° = 0). It is written as E°.

EMF of Daniell cell

Cell: Zn | Zn²⁺ (0.001 M) || Cu²⁺ (0.1 M) | Cu

Anode   : Zn → Zn²⁺ + 2e⁻
Cathode : Cu²⁺ + 2e⁻ → Cu
Cell    : Zn + Cu²⁺ → Zn²⁺ + Cu      (n = 2)

E = E° − (0.0591/n) log ([Zn²⁺]/[Cu²⁺])
  = 1.2 − 0.02955 × log (0.001/0.1)
  = 1.2 − 0.02955 × (−2)
  = 1.2 + 0.0591 = 1.259 V

Answer: EMF ≈ 1.26 V. (The given standard potential 1.2 V is used as stated; the usual textbook value is 1.10 V.)

✓ Answer checked by Claude Opus 5.5 (high effort)

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