---
title: "Single electrode potential and its measurement"
subject: "Engineering Chemistry"
chapter: 1
key: "semester_2/engineering_chemistry:single-electrode-potential"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/single-electrode-potential
site: BCT Engineering
---

# Single electrode potential and its measurement

Engineering Chemistry · Chapter 1: Electro-chemistry and Buffer

- Asked in: 2074 Bhadra, 1+4 marks
- Video: [Electrode Potential and Standard Hydrogen Electrode](https://www.youtube.com/watch?v=2tgIDC-i9LI) — Najam Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/single-electrode-potential
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-1

## Question

What is single electrode potential? Can its absolute value be measured? If not, how is the problem solved? Describe with a suitable example.

## Short answer

Single electrode potential is the potential difference at a metal–solution interface. Its absolute value cannot be measured because a voltmeter requires two electrodes. The problem is solved by using a standard hydrogen electrode (SHE) as reference, assigning it 0.00 V, and measuring cell emf; e.g., Zn/Zn²⁺ with SHE gives -0.76 V.

## Answer

#### Single electrode potential
The potential difference set up between a metal and the solution of its own ions at the metal–solution interface is called the **single electrode potential**. It arises because a metal M dipped in a solution of Mⁿ⁺ either loses ions to the solution (M → Mⁿ⁺ + ne⁻, so the metal becomes negative) or ions deposit on it (Mⁿ⁺ + ne⁻ → M, so the metal becomes positive), giving an electrical double layer.

#### Can its absolute value be measured?
No. An electrode potential is a potential difference across one interface. To measure it we must connect a voltmeter, which needs a second electrode and thus a second interface. The voltmeter always gives the difference of two electrode potentials, never one alone.

#### How the problem is solved
A reference electrode of arbitrarily assigned potential is used: the **standard hydrogen electrode (SHE)**, Pt, H₂ (1 atm) | H⁺ (1 M), whose potential is fixed as 0.00 V. The electrode to be measured is coupled with SHE and the cell emf is measured. This emf is taken as the electrode potential of the unknown electrode on the hydrogen scale.

**Example: Zn electrode**
```text
Zn | Zn²⁺ (1 M) || H⁺ (1 M) | H₂ (1 atm), Pt
```
- Anode: Zn → Zn²⁺ + 2e⁻
- Cathode: 2H⁺ + 2e⁻ → H₂
- Measured emf = 0.76 V = E°(cathode) − E°(anode) = 0 − E°(Zn²⁺/Zn)

So **E°(Zn²⁺/Zn) = −0.76 V** (reduction potential). Similarly, for Cu with SHE, E°(Cu²⁺/Cu) = +0.34 V. The values are therefore relative to SHE, not absolute.

## Check yourself

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

1. Single electrode potential arises because:
   A. Two different metals touch each other
   B. A metal in its ion solution forms an electrical double layer at the interface
   C. Hydrogen gas dissolves in the metal
   D. The solution evaporates
   Answer: B. Loss of ions to solution or deposition of ions on the metal sets up a double layer whose potential difference is the electrode potential. (Key point: Definition and origin)

2. Why can the absolute value of a single electrode potential not be measured?
   A. Metals have no potential
   B. A voltmeter needs a second electrode, so it only gives a difference of two potentials
   C. Temperature changes it constantly
   D. Solutions are non-conducting
   Answer: B. Any measurement needs a second electrode and interface, so only a potential difference is obtained. (Key point: Why absolute value cannot be measured)

3. How is the problem solved?
   A. By using an electrode with zero resistance
   B. By coupling with a reference electrode (SHE) assigned 0.00 V
   C. By measuring at absolute zero
   D. By using a larger voltmeter
   Answer: B. SHE is arbitrarily given 0 V, and the cell emf with it is taken as the electrode potential on the hydrogen scale. (Key point: The solution to the problem)

4. In Zn | Zn2+ || H+ | H2 the emf is 0.76 V. What is E°(Zn2+/Zn)?
   A. +0.76 V
   B. -0.76 V
   C. 0 V
   D. +1.52 V
   Answer: B. E°cell = E°(cathode) - E°(anode) = 0 - E°(Zn) = 0.76, so E°(Zn2+/Zn) = -0.76 V. (Key point: Zn example)

## Related in Engineering Chemistry

- [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
- [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
- [Non-standard electrode potential; Fe/Ag cell emf](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Anonstandard-emf-fe-ag) — Engineering Chemistry, chapter 1
- [Electrode potential origin; Zn reduction potential](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aelectrode-potential-zn) — 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
- [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

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