---
title: "Single electrode potential; Ni/Ag cell EMF"
subject: "Engineering Chemistry"
chapter: 1
key: "semester_2/engineering_chemistry:ni-ag-cell"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/ni-ag-cell
site: BCT Engineering
---

# Single electrode potential; Ni/Ag cell EMF

Engineering Chemistry · Chapter 1: Electro-chemistry and Buffer

- Asked in: 2071 Magh, 2+3 marks
- Video: [Cell Potential Problems - Electrochemistry](https://www.youtube.com/watch?v=UzkLP8segcs) — The Organic Chemistry Tutor
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/ni-ag-cell
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-1

## Question

How is single electrode potential originate? From the given electrode system, answer the following questions.
Ni → Ni²⁺ + 2e⁻  E° = +0.25 V
Ag → Ag⁺ + e⁻  E° = −0.80 V
[Ni²⁺] = 0.8 M, [Ag⁺] = 0.2 M, R = 8.314 JK⁻¹mol⁻¹
a) Which of the given electrodes acts as anode and why?
b) Construct a galvanic cell using proper cell notation when the given electrodes are coupled.
c) Calculate the EMF of the cell at 27°C.

## Short answer

Single electrode potential originates from the equilibrium of metal dissolution and ion deposition forming a double layer. Ni has higher oxidation potential and is anode. Cell: Ni | Ni2+ (0.8 M) || Ag+ (0.2 M) | Ag. EMF at 27°C = 1.05 – (0.01292) ln(20) = 1.01 V.

## Answer

#### Origin of single electrode potential
When a metal M is dipped in a solution of its ions Mⁿ⁺, two processes occur: M → Mⁿ⁺ + ne⁻ (metal becomes negatively charged) and Mⁿ⁺ + ne⁻ → M (metal becomes positively charged). At equilibrium an electrical double layer forms at the interface, and the potential difference across it is the single electrode potential.

The values given are oxidation potentials: Ni +0.25 V, Ag −0.80 V.

#### a) Anode
Ni has the higher oxidation potential (+0.25 V > −0.80 V), so it is oxidised more easily. **Ni is the anode**; Ag is the cathode.

#### b) Cell notation
Ni | Ni²⁺ (0.8 M) || Ag⁺ (0.2 M) | Ag

```text
Anode   : Ni → Ni²⁺ + 2e⁻
Cathode : 2Ag⁺ + 2e⁻ → 2Ag
Cell    : Ni + 2Ag⁺ → Ni²⁺ + 2Ag    (n = 2)
```

#### c) EMF at 27°C (300 K)
```text
E°cell = 0.25 + 0.80 = 1.05 V
Q = [Ni²⁺]/[Ag⁺]² = 0.8/(0.2)² = 20
RT/nF = 8.314 × 300/(2 × 96500) = 0.01292 V
E = E° − (RT/nF) ln Q = 1.05 − 0.01292 × 2.996
  = 1.05 − 0.0387 = 1.011 V
```
**Answer: EMF ≈ 1.01 V.**

## Check yourself

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

1. Ni oxidation +0.25 V and Ag oxidation -0.80 V. Which is the anode?
   A. Ag, since it is a noble metal
   B. Ni, but only if its concentration is higher
   C. Neither
   D. Ni, since it has the higher oxidation potential (+0.25 V > -0.80 V)
   Answer: D. Higher oxidation potential (+0.25 > -0.80) means Ni is oxidised more easily, so it is the anode. (Key point: Anode selection)

2. Net reaction is:
   A. Ni + Ag+ -> Ni2+ + Ag
   B. Ni2+ + 2Ag -> Ni + 2Ag+
   C. 2Ni + Ag+ -> 2Ni2+ + Ag
   D. Ni + 2Ag+ -> Ni2+ + 2Ag
   Answer: D. Ni gives 2e-, which are taken by 2 Ag+. (Key point: Cell reaction)

3. E°cell = ?
   A. 0.55 V
   B. -1.05 V
   C. 0.80 V
   D. 1.05 V
   Answer: D. E°cell = 0.25 + 0.80 = 1.05 V (oxidation + reduction). (Key point: Standard emf)

4. Q = 0.8/(0.2)^2 = 20, RT/nF = 0.01292 V. E is about:
   A. 1.05 V
   B. 0.96 V
   C. 1.09 V
   D. 1.01 V
   Answer: D. E = 1.05 - 0.01292 x ln 20 (2.996) = 1.05 - 0.0387 = 1.011 V. (Key point: Final EMF)

## Related in Engineering Chemistry

- [Ni/Cd galvanic cell: electrodes, emf](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ani-cd-cell) — 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
- [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
- [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
- [Normal hydrogen electrode; Ni/Cu cell emf](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Anhe-ni-cu-cell) — Engineering Chemistry, chapter 1
- [Standard hydrogen electrode; Mg/Ag cell emf](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ashe-mg-ag-cell) — Engineering Chemistry, chapter 1