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

# IUPAC names of two complexes

Engineering Chemistry · Chapter 6: Coordination Complexes

- Asked in: 2069 Bhadra, 2.5 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-2069
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-6

## Question

Write the IUPAC name of the following co-ordination compounds.
(i) K[PtCl₅(NH₃)]
(ii) [Co(NH₃)₅SO₄]Br

## Short answer

(i) potassium amminepentachloroplatinate(IV), (ii) pentaamminesulfatocobalt(III) bromide.

## Answer

(i) K[PtCl₅(NH₃)]: **potassium amminepentachloroplatinate(IV)** (x − 5 = −1, so x = +4)
(ii) [Co(NH₃)₅SO₄]Br: **pentaamminesulfatocobalt(III) bromide** (the sulfate is inside the sphere; x + 0 − 2 = +1, so x = +3)

## Check yourself

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

1. What is the oxidation state of Pt in K[PtCl5(NH3)]?
   A. +2
   B. +3
   C. +4
   D. +5
   Answer: C. x + 5(-1) + 0 = -1 gives x = +4. (Key point: Oxidation state of Pt)

2. Which is the correct name of K[PtCl5(NH3)]?
   A. Potassium amminepentachloroplatinate(IV)
   B. Potassium pentachloroammineplatinum(IV)
   C. Pentachloroamminepotassium platinate(IV)
   D. Potassium amminepentachloroplatinate(II)
   Answer: A. Ligands are alphabetical (ammine before chloro), and an anionic complex ends in -ate. (Key point: Name of K[PtCl5(NH3)])

3. In [Co(NH3)5SO4]Br, why is sulfato named as a ligand while bromide is named separately?
   A. Bromide is a neutral ligand
   B. Sulfate is always a counter ion
   C. Both are inside the sphere
   D. Sulfate is inside the coordination sphere, bromide is outside as the counter ion
   Answer: D. The bracket holds the complex ion, so SO4 is a ligand, while Br- ionises outside. (Key point: Sulfate in [Co(NH3)5SO4]Br)

4. What is the oxidation state of Co in [Co(NH3)5SO4]Br?
   A. +2
   B. +3
   C. +1
   D. +4
   Answer: B. The complex cation is +1: x + 0 - 2 = +1, so x = +3; name pentaamminesulfatocobalt(III) bromide. (Key point: Co oxidation state)

## Close variants set in other exams

- [IUPAC names of four complexes](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aiupac-names-2070) — Engineering Chemistry, chapter 6, asked 4×
- [IUPAC names of four complexes](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aiupac-names-2070m) — Engineering Chemistry, chapter 6, asked 4×
- [IUPAC names of four complexes](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aiupac-names-2072m) — Engineering Chemistry, chapter 6, asked 4×

## Related in Engineering Chemistry

- [IUPAC names and EAN of complexes](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aiupac-ean) — Engineering Chemistry, chapter 6
- [IUPAC names of four complexes](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aiupac-names-2072) — Engineering Chemistry, chapter 6
- [IUPAC names of four complexes](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aiupac-names-2069p) — Engineering Chemistry, chapter 6
- [IUPAC names of four complexes](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aiupac-names-2067m) — Engineering Chemistry, chapter 6
- [Chelate, Sidgwick theory, IUPAC names](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Achelate-sidgwick) — Engineering Chemistry, chapter 6
- [Principal and auxiliary valencies; IUPAC names](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aprimary-secondary-valency) — 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