---
title: "TiO₂ white but TiCl₃ violet"
subject: "Engineering Chemistry"
chapter: 5
key: "semester_2/engineering_chemistry:tio2-ticl3-colour"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/tio2-ticl3-colour
site: BCT Engineering
---

# TiO₂ white but TiCl₃ violet

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

- Asked in: 2071 Bhadra, 2.5 marks; 2067 Mangsir, 2 marks (asked 2 times)
- Video: [Explain the violet colour of the complex \( \left[\mathrm{Ti}\left(...](https://www.youtube.com/watch?v=ApIjGjozeSQ) — PW Solutions
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/tio2-ticl3-colour
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-5

## Question

Give reason: TiO₂ is white but TiCl₃ is violet.

## Short answer

TiO₂ contains Ti⁴⁺ (3d⁰), so no d–d transition occurs; it reflects all visible light and appears white. TiCl₃ contains Ti³⁺ (3d¹); in aqueous [Ti(H₂O)₆]³⁺ the d electron absorbs green-yellow light, transmitting the complementary violet colour.

## Answer

- **TiO₂ is white:** titanium is in the +4 state, Ti⁴⁺ is 3d⁰. There are no d electrons, so no d–d transition is possible and visible light is not absorbed (all wavelengths reflected), giving white.
- **TiCl₃ is violet:** titanium is in the +3 state, Ti³⁺ is 3d¹. In solution as [Ti(H₂O)₆]³⁺ the single d electron lies in the t₂g level. It absorbs green-yellow light (around 500 nm) to jump to the e_g level, and the complementary violet (purple) colour is seen.

## Check yourself

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

1. Why is TiO2 white?
   A. Ti4+ is 3d0, so no d–d transition
   B. Ti4+ is 3d1
   C. It absorbs all light
   D. It has unpaired electrons
   Answer: A. No d electrons means no visible light absorbed. (Key point: TiO2)

2. Why is TiCl3 coloured?
   A. Ti3+ is 3d0
   B. Ti3+ is 3d1 and its d electron undergoes d–d transition
   C. Ti3+ is 3d10
   D. Cl- absorbs all light
   Answer: B. t2g to eg excitation absorbs visible light. (Key point: TiCl3)

3. TiCl3 absorbs green-yellow light, so it looks
   A. Green
   B. White
   C. Violet
   D. Yellow
   Answer: C. The complementary colour is seen. (Key point: Complementary)