---
title: "Colour of Ti³⁺ compounds vs zinc compounds"
subject: "Engineering Chemistry"
chapter: 5
key: "semester_2/engineering_chemistry:ti3-zn-colour"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/ti3-zn-colour
site: BCT Engineering
---

# Colour of Ti³⁺ compounds vs zinc compounds

Engineering Chemistry · Chapter 5: 3-d Transition Elements and their Applications

- Asked in: 2074 Bhadra, 2 marks
- Video: [Predict Which of the Following Ions are Coloured in Aqueous Solution? Cu⁺, Sc³⁺, Fe²⁺, Ti³⁺, Zn²⁺ |](https://www.youtube.com/watch?v=n2PoD9BXRRo) — Cracking BSc & 12th Chemistry
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/ti3-zn-colour
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-5

## Question

Explain why compounds of Ti³⁺ are coloured but those of zinc are colourless.

## Short answer

Ti3+ (3d1) has a d–d transition, absorbing green-yellow light and appearing violet. Zn2+ (3d10) has a filled d subshell with no vacant orbital for electron excitation, so no visible light is absorbed and compounds are colourless.

## Answer

- **Ti³⁺** is 3d¹: it has one d electron in the t₂g level, which absorbs visible light (about 500 nm) and jumps to the e_g level (d–d transition), so the complementary violet colour is seen.
- **Zinc compounds (Zn²⁺)** are 3d¹⁰: the d subshell is completely filled, with no vacant d orbital to which an electron can be excited, so no visible light is absorbed and the compounds are colourless (white).

## Check yourself

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

1. Why is Ti3+ coloured?
   A. It has 3d10
   B. It has no d electrons
   C. Its single 3d electron absorbs visible light in a d–d transition
   D. It has many s electrons
   Answer: C. t2g to eg excitation. (Key point: Ti3+)

2. Why is Zn2+ colourless?
   A. 3d1
   B. 3d9
   C. 3d0 with absorption
   D. 3d10 is full, no vacant d orbital for excitation
   Answer: D. No visible light is absorbed. (Key point: Zn2+)

3. Ti3+ appears
   A. Violet
   B. Green
   C. White
   D. Blue
   Answer: A. It absorbs about 500 nm; violet is complementary. (Key point: Ti3+ colour)

## Related in Engineering Chemistry

- [Colour of Ti³⁺ vs Ti⁴⁺ compounds](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ati3-ti4-colour) — Engineering Chemistry, chapter 5
- [Colour of vanadium +5 vs +3 compounds](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Av5-v3-colour) — Engineering Chemistry, chapter 5