---
title: "Complex ion and ligands in [Co(NH₃)₆]Cl₃"
subject: "Engineering Chemistry"
chapter: 6
key: "semester_2/engineering_chemistry:identify-complex-ion-ligands"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/identify-complex-ion-ligands
site: BCT Engineering
---

# Complex ion and ligands in [Co(NH₃)₆]Cl₃

Engineering Chemistry · Chapter 6: Coordination Complexes

- Asked in: 2067 Chaitra, 2 marks
- Video: [Basic Terms|Coordination number|Complex Ion|Central Atom|Ion|Ligands|Coordination sphere #chemistry](https://www.youtube.com/watch?v=RTnTuqPDLYE) — Xplore The World of Chemistry
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/identify-complex-ion-ligands
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-6

## Question

Identify the complex ion and ligands in the compound [Co(NH₃)₆]Cl₃.

## Short answer

Complex ion: [Co(NH₃)₆]³⁺ (hexaamminecobalt(III) ion). Ligands: six neutral NH₃ molecules; coordination number 6. Counter ions: three Cl⁻.

## Answer

In [Co(NH₃)₆]Cl₃:
- **Complex ion:** [Co(NH₃)₆]³⁺ (hexaamminecobalt(III) ion), the part inside the square bracket.
- **Ligands:** six neutral ammonia (NH₃) molecules, each donating a lone pair on N to Co³⁺.
- Central metal ion: Co³⁺; coordination number 6.
- Counter ions: three Cl⁻ outside the bracket, which ionise and precipitate with AgNO₃.

## Check yourself

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

1. Which is the complex ion in [Co(NH3)6]Cl3?
   A. Cl-
   B. Co3+ only
   C. [Co(NH3)6]3+
   D. NH3
   Answer: C. The part inside the square bracket is the complex ion. (Key point: Complex ion)

2. What are the ligands?
   A. Six neutral NH3 molecules donating lone pairs from N
   B. Three Cl-
   C. Co3+
   D. Six Cl-
   Answer: A. NH3 donates lone pairs to Co3+. (Key point: Ligands)

3. What happens to the three Cl- outside the bracket?
   A. They stay bound to Co
   B. They are ligands
   C. They do not ionise
   D. They ionise and precipitate with AgNO3
   Answer: D. Outside ions ionise in water. (Key point: Counter ions)

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