---
title: "IUPAC names of four complexes"
subject: "Engineering Chemistry"
chapter: 6
key: "semester_2/engineering_chemistry:iupac-names-2069p"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/iupac-names-2069p
site: BCT Engineering
---

# IUPAC names of four complexes

Engineering Chemistry · Chapter 6: Coordination Complexes

- Asked in: 2069 Poush, 2 marks
- Video: [Naming Coordination Compounds - Chemistry](https://www.youtube.com/watch?v=yeNtqjE0dJw) — 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/iupac-names-2069p
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-6

## Question

Write down the IUPAC names of the followings:
i) [Cr(H₂O)₄Cl₂]Cl
ii) K₃[Al(C₂O₄)₃]
iii) [Co(NH₃)₃Cl₃]
iv) [HgI₄]²⁻

## Short answer

i) tetraaquadichlorochromium(III) chloride, ii) potassium trioxalatoaluminate(III), iii) triamminetrichlorocobalt(III), iv) tetraiodomercurate(II) ion.

## Answer

i) [Cr(H₂O)₄Cl₂]Cl: **tetraaquadichlorochromium(III) chloride**
ii) K₃[Al(C₂O₄)₃]: **potassium trioxalatoaluminate(III)**
iii) [Co(NH₃)₃Cl₃]: **triamminetrichlorocobalt(III)**
iv) [HgI₄]²⁻: **tetraiodomercurate(II) ion**

## Check yourself

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

1. What is the name of [Cr(H2O)4Cl2]Cl?
   A. Dichlorotetraaquachromium(III) chloride
   B. Tetraaquadichlorochromium(III) chloride
   C. Tetraaquadichlorochromate(III) chloride
   D. Tetrahydrodichlorochromium(II) chloride
   Answer: B. Aqua precedes chloro alphabetically, the complex cation is not -ate, and Cr is +3. (Key point: Name of [Cr(H2O)4Cl2]Cl)

2. What is the name of K3[Al(C2O4)3]?
   A. Potassium aluminiumtrioxalate(III)
   B. Tripotassium oxalatoaluminium
   C. Potassium trioxalatoaluminium(III)
   D. Potassium trioxalatoaluminate(III)
   Answer: D. The anionic complex takes -ate (aluminate) with Al +3 and three oxalato ligands. (Key point: Name of K3[Al(C2O4)3])

3. What is the name of the neutral complex [Co(NH3)3Cl3]?
   A. Triamminetrichlorocobalt(III)
   B. Trichlorotriamminecobaltate(III)
   C. Triamminetrichlorocobalt(II)
   D. Triamminetrichlorocobaltate(III)
   Answer: A. A neutral complex has no ending change, ligands are alphabetical, and Co is +3. (Key point: Neutral complex name)

4. What is the name of [HgI4]2-?
   A. Tetraiodomercury(II) ion
   B. Mercurytetraiodide(II)
   C. Tetraiodomercurate(II) ion
   D. Tetraiodomercurate(IV) ion
   Answer: C. It is an anion so mercurate is used; Hg is +2 since x - 4 = -2. (Key point: Name of [HgI4]2-)

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