Transition Metals & Complex Ions
20min Part 3 / Ch6 / Lesson 3
Objectives
- Describe the characteristics of transition metals
- Know the names and colors of common complex ions
- Understand the systematic separation of metal ions
Characteristics of Transition Metals
Transition metals (Groups 3–11) share common features:
- Variable oxidation states (Fe²⁺/Fe³⁺, Cu⁺/Cu²⁺, etc.)
- Colored compounds are common
- Many serve as catalysts (Fe, Pt, V₂O₅, MnO₂, etc.)
- Form complex ions readily
Iron Compounds
| Property | Fe²⁺ (iron(II)) | Fe³⁺ (iron(III)) |
|---|---|---|
| Solution color | Pale green | Yellow-brown |
| Hydroxide | Fe(OH)₂ (green-white) | Fe(OH)₃ (red-brown) |
| With KSCN | No change | Blood-red |
| With K₄[Fe(CN)₆] | Dark blue precipitate (Turnbull’s blue) | Dark blue precipitate |
| With K₃[Fe(CN)₆] | Dark blue precipitate | No change (brown) |
Comparing Fe²⁺ and Fe³⁺
Copper Compounds
| Compound | Color | Notes |
|---|---|---|
| CuSO₄ (anhydrous) | White | Used to detect water |
| CuSO₄·5H₂O | Blue | Blue vitriol |
| Cu(OH)₂ | Blue-white | Heated → CuO (black) |
| CuO | Black | Copper(II) oxide |
| Cu₂O | Red | Formed in Fehling’s test |
Complex Ions
Complex ions: metal ions bonded to ligands via coordinate bonds.
Key examples:
| Complex ion | Color | Formation |
|---|---|---|
| [Cu(NH₃)₄]²⁺ | Deep blue | Cu²⁺ + excess NH₃ |
| [Ag(NH₃)₂]⁺ | Colorless | Ag⁺ + NH₃ → AgCl dissolves |
| [Zn(OH)₄]²⁻ | Colorless | Zn²⁺ + excess NaOH |
| [Al(OH)₄]⁻ | Colorless | Al³⁺ + excess NaOH |
| [Fe(CN)₆]⁴⁻ | Yellow | Fe²⁺ + CN⁻ |
Systematic Separation of Metal Ions
Check Your Understanding
Q1 What color forms when KSCN is added to Fe³⁺ solution?
Q2 What happens when excess NH₃ is added to Cu²⁺?
Q3 What color is anhydrous CuSO₄?
Exercises
Q1. Describe how to separate Ag⁺, Cu²⁺, and Fe³⁺ from a mixed solution.
Solution
- Add HCl → AgCl (white) precipitates. Filter to separate Ag⁺.
- To the filtrate, pass H₂S (acidic conditions) → CuS (black) precipitates. Filter to separate Cu²⁺.
- Boil to remove H₂S, then add NaOH → Fe(OH)₃ (red-brown) precipitates. Fe³⁺ is separated.