---
title: "Colour of Ti³⁺ vs Ti⁴⁺ compounds"
subject: "Engineering Chemistry"
chapter: 5
key: "semester_2/engineering_chemistry:ti3-ti4-colour"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/ti3-ti4-colour
site: BCT Engineering
---

# Colour of Ti³⁺ vs Ti⁴⁺ compounds

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

- Asked in: 2072 Asoj, 2.5 marks
- Video: [Why Are Ti³⁺ Salts Coloured but Ti⁴⁺ Salts Colourless? | Transition Elements Explained](https://www.youtube.com/watch?v=9yJRC0NF39w) — 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-ti4-colour
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-5

## Question

Explain why: Compounds of Titanium in +3 oxidation state are coloured but those in +4 oxidation state are colourless.

## Short answer

Ti(III) is 3d1, so a d–d transition absorbs visible light, giving a violet colour. Ti(IV) is 3d0 with no d electrons, so no d–d transition occurs and compounds are colourless.

## Answer

Colour in transition metal compounds comes from d–d transitions: an electron in a lower-energy d orbital absorbs visible light and jumps to a higher-energy d orbital of the split d set.

- Ti³⁺ has the configuration 3d¹. In water it forms [Ti(H₂O)₆]³⁺ with the single electron in a t₂g orbital. It absorbs light (about 500 nm, green–yellow) and jumps to e_g, so the complex looks violet (purple).
- Ti⁴⁺ has the configuration 3d⁰. There is no d electron to excite, so no d–d transition is possible and no visible light is absorbed. Its compounds (TiO₂, TiCl₄) are colourless or white.

Hence Ti(III) compounds are coloured and Ti(IV) compounds are colourless.

## Check yourself

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

1. What causes the colour of transition metal compounds?
   A. d-d transitions of an electron from a lower to a higher split d orbital absorbing visible light
   B. Emission of light when electrons fall to the ground state
   C. Transfer of electrons between s and p orbitals
   D. Scattering of light by the metal lattice
   Answer: A. An electron absorbs visible light and jumps between split d levels; the transmitted light is the colour seen. (Key point: Origin of colour)

2. Why is [Ti(H2O)6]3+ coloured?
   A. It is 3d0, so it has many vacant orbitals
   B. It is 3d1, so the single t2g electron can jump to e_g by absorbing visible light
   C. It is 3d10, so it has paired electrons
   D. It has no d electrons, so it absorbs all light
   Answer: B. Ti3+ has one d electron which can be excited t2g to e_g, absorbing about 500 nm and appearing violet. (Key point: Ti3+ configuration)

3. Why are Ti(IV) compounds such as TiO2 and TiCl4 colourless?
   A. Ti4+ is 3d10 and all orbitals are full
   B. Ti4+ has unpaired electrons that cancel colour
   C. Ti4+ is 3d0, so no d electron is available for a d-d transition
   D. Ti4+ absorbs all visible light equally
   Answer: C. With no d electrons, no d-d transition can occur, so no visible light is absorbed. (Key point: Ti4+ colourless)

## Related in Engineering Chemistry

- [Colour of Ti³⁺ compounds vs zinc compounds](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ati3-zn-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