---
title: "Formulae of six named complexes"
subject: "Engineering Chemistry"
chapter: 6
key: "semester_2/engineering_chemistry:write-formulae-2067c"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/write-formulae-2067c
site: BCT Engineering
---

# Formulae of six named complexes

Engineering Chemistry · Chapter 6: Coordination Complexes

- Asked in: 2067 Chaitra, 3 marks
- Video: [Coordination Compounds: Geometry and Nomenclature](https://www.youtube.com/watch?v=Hs5JBjX51dc) — Professor Dave Explains
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/write-formulae-2067c
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-6

## Question

Write the formulae of the following co-ordination compounds.
a) Dichloro tetra-aquo chromium (III) cation
b) Tris (ethylene diamine) chromium(III) chloride
c) Dicyano argentate (I) ion
d) Bromo penta-ammine cobalt (III) sulfate
e) Sod. hexa nitrito cobaltate(III)
f) Hexa-cyanoferrate (III) ion

## Short answer

a) [Cr(H₂O)₄Cl₂]⁺; b) [Cr(en)₃]Cl₃; c) [Ag(CN)₂]⁻; d) [Co(NH₃)₅Br]SO₄; e) Na₃[Co(NO₂)₆]; f) [Fe(CN)₆]³⁻.

## Answer

a) Dichlorotetraaquachromium(III) cation: **[Cr(H₂O)₄Cl₂]⁺**
b) Tris(ethylenediamine)chromium(III) chloride: **[Cr(en)₃]Cl₃**
c) Dicyanoargentate(I) ion: **[Ag(CN)₂]⁻**
d) Bromopentaamminecobalt(III) sulfate: **[Co(NH₃)₅Br]SO₄**
e) Sodium hexanitritocobaltate(III): **Na₃[Co(NO₂)₆]**
f) Hexacyanoferrate(III) ion: **[Fe(CN)₆]³⁻**

## Check yourself

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

1. What is dichlorotetraaquachromium(III) cation?
   A. [Cr(H2O)4Cl2]3+
   B. [Cr(H2O)4Cl2]+
   C. [Cr(H2O)2Cl4]+
   D. [Cr(H2O)4Cl2]-
   Answer: B. +3 + 2(-1) = +1. (Key point: Formula a)

2. What is dicyanoargentate(I) ion?
   A. [Ag(CN)2]+
   B. [Ag(CN)2]-
   C. [Ag(CN)]-
   D. [Ag(CN)2]2-
   Answer: B. +1 + 2(-1) = -1. (Key point: Formula c)

3. What is bromopentaamminecobalt(III) sulfate?
   A. [Co(NH3)5Br]2SO4
   B. [Co(NH3)5]BrSO4
   C. [Co(NH3)5SO4]Br
   D. [Co(NH3)5Br]SO4
   Answer: D. Co3+ + Br- = 2+, balanced by one SO4 2-. (Key point: Formula d)

4. What is sodium hexanitritocobaltate(III)?
   A. Na3[Co(NO2)6]
   B. Na[Co(NO2)6]
   C. Na6[Co(NO2)6]
   D. Na3[Co(NO2)3]
   Answer: A. Co3+ + 6(-1) = -3, so 3 Na+. (Key point: Formula e)

## Related in Engineering Chemistry

- [Formulae of six named complexes](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awrite-formulae-2068m) — Engineering Chemistry, chapter 6
- [Formulae of named complexes](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awrite-formulae-complexes) — Engineering Chemistry, chapter 6
- [Define co-ordination number with example](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Adefine-coordination-number) — Engineering Chemistry, chapter 6
- [Complex ion and ligands in [Co(NH₃)₆]Cl₃](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aidentify-complex-ion-ligands) — Engineering Chemistry, chapter 6

## Related in other subjects

- [Define co-ordination in protection](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Adefine-coordination) — Switchgear and Protection, chapter 1