---
title: "Electrode potential origin; Zn reduction potential"
subject: "Engineering Chemistry"
chapter: 1
key: "semester_2/engineering_chemistry:electrode-potential-zn"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/electrode-potential-zn
site: BCT Engineering
---

# Electrode potential origin; Zn reduction potential

Engineering Chemistry · Chapter 1: Electro-chemistry and Buffer

- Asked in: 2071 Bhadra, 1+1+3 marks
- Video: [Electrode Potentials: How They Work and Why They Matter!](https://www.youtube.com/watch?v=aJG_yAe6hLA) — Chemistry Student
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/electrode-potential-zn
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-1

## Question

What is electrode potential? How does it originate? What will be the reduction potential of Zn²⁺/Zn electrode when zinc metal in contact with 0.1 M H₂SO₄ at 25°C. Given E°Zn/Zn²⁺ = +0.768 V.

## Short answer

Electrode potential is the potential difference between a metal and its ion solution due to the electrical double layer at equilibrium. Zn2+/Zn reduction potential: E = -0.768 + (0.0591/2) log(0.1) = -0.80 V.

## Answer

#### Electrode potential
The potential difference developed between a metal and the solution of its own ions at their interface, due to the tendency of the metal to lose or gain electrons.

#### Origin
A metal rod in a solution of its ions has two opposite tendencies. Metal atoms may go into solution as ions, leaving electrons on the rod (M → Mⁿ⁺ + ne⁻), so the rod becomes negative and attracts positive ions around it. Or ions of the solution may take electrons from the rod and deposit as metal, making the rod positive. Dynamic equilibrium is reached and an electrical double layer forms; the potential difference across it is the electrode potential.

#### Reduction potential of Zn²⁺/Zn
Reading: the question's "0.1 M H₂SO₄" has no Zn²⁺ given; I take the zinc in contact with 0.1 M Zn²⁺ solution (ZnSO₄). E°Zn/Zn²⁺ = +0.768 V is an oxidation potential, so E°(Zn²⁺/Zn) = −0.768 V.
```text
Zn²⁺ + 2e⁻ → Zn
E = E° + (0.0591/n) log [Zn²⁺]
  = −0.768 + (0.0591/2) log (0.1)
  = −0.768 − 0.0296
  = −0.7976 V
```
**Answer: E(Zn²⁺/Zn) ≈ −0.80 V.**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does a metal-solution electrode potential originate?
   A. Water decomposes at the surface
   B. The metal melts
   C. Electrons leave the solution
   D. Metal ions go into solution leaving electrons, or ions deposit, forming an electrical double layer
   Answer: D. Equilibrium between dissolution and deposition produces charge separation (double layer) across the interface. (Key point: Origin of potential)

2. E°(Zn/Zn2+) = +0.768 V is an oxidation potential. E°(Zn2+/Zn) is:
   A. +0.768 V
   B. 0 V
   C. +1.536 V
   D. -0.768 V
   Answer: D. Reduction potential is the negative of oxidation potential. (Key point: Converting potentials)

3. Which is the Nernst equation used for Zn2+ + 2e- -> Zn at 25°C?
   A. E = E° - (0.0591/2) log [Zn2+]
   B. E = E° + 0.0591 log [Zn2+]
   C. E = E° + 2 log [Zn2+]
   D. E = E° + (0.0591/2) log [Zn2+]
   Answer: D. For reduction Mn+ + ne- -> M, E = E° + (0.0591/n) log[Mn+]. (Key point: Nernst equation)

4. With [Zn2+] = 0.1 M, E is:
   A. -0.738 V
   B. -0.768 V
   C. +0.80 V
   D. -0.80 V
   Answer: D. E = -0.768 + 0.02955 x (-1) = -0.7976, about -0.80 V. (Key point: Final value)

## Related in Engineering Chemistry

- [Electrode potential origin; Zn-Cu cell notation](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aelectrode-potential-zn-cu) — Engineering Chemistry, chapter 1
- [Electrode potential; Cu/Ag cell EMF](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aelectrode-potential-cell-emf) — Engineering Chemistry, chapter 1
- [Single electrode potential; Ni/Ag cell EMF](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ani-ag-cell) — Engineering Chemistry, chapter 1
- [Standard electrode potential; Daniell cell EMF](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Adaniell-cell-emf) — Engineering Chemistry, chapter 1
- [Standard electrode potential; Fe/Ni cell emf](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Afe-ni-cell) — Engineering Chemistry, chapter 1
- [Single electrode potential and its measurement](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Asingle-electrode-potential) — Engineering Chemistry, chapter 1