Ever wondered why copper sulfate appears blue or why lead iodide turns yellow? The color of inorganic salts and compounds is not just for aesthetics — it’s a critical concept in inorganic chemistry, especially for competitive exams like NEET, JEE, and Olympiads.
This guide helps you understand:
- Common colored compounds
- Their chemical formulae
- Color memory tricks
- Visual recognition for exams
Why Do Compounds Have Colors?
Colors in compounds arise due to:
- d–d transitions in transition metals
- Charge Transfer Complexes (CTCs)
- Metal-ligand interactions in coordination compounds
Transition metals with partially filled d-orbitals absorb specific wavelengths of light, and reflect the complementary color — which we see.
List of Common Colored Compounds and Their Colors
Here is a categorized list of 30+ common salts, oxides, and compounds along with their characteristic colors:
⚪ White Compounds
| Compound | Color |
|---|---|
| AgCl (Silver chloride) | White |
| MgO (Magnesium oxide) | White |
| BaSO₄ (Barium sulfate) | White |
| Pb(NO₃)₂ (Lead nitrate) | White |
| PbSO₄ (Lead sulfate) | White |
| PbCl₂ (Lead chloride) | White |
| ZnCl₂ (Zinc chloride) | White |
| MgCl₂ (Magnesium chloride) | White |
| K₂SO₄ (Potassium sulfate) | White |
| Na₂SO₄ (Sodium sulfate) | White |
| CaCO₃ (Calcium carbonate) | White |
| BaCl₂ (Barium chloride) | White |
| NaCl (Sodium chloride) | White |
| AgNO₃ (Silver nitrate) | Colorless (solution) |
🧠 Mnemonic: "BAAPS ZKM CaNa" — Ba, Ag, Al, Pb, SO₄, Zn, K, Mg, Ca, Na = mostly white salts
🔵 Blue and Green Compounds
| Compound | Color |
|---|---|
| CuSO₄ (Copper(II) sulfate) | Blue |
| CuCl₂ (Copper(II) chloride) | Bluish green |
| FeSO₄ (Ferrous sulfate) | Green |
| Ni²⁺ (Nickel ion) | Green |
| Cr³⁺ (Chromium ion) | Green |
| Cu²⁺ ion | Blue |
🧠 Mnemonic: "CuCrNiFe" — Copper, Chromium, Nickel, Ferrous → Cool Blue-Green shades
🟡 Yellow Compounds
| Compound | Color |
|---|---|
| PbI₂ (Lead iodide) | Yellow |
| PbO (Lead oxide) | Yellow |
| Fe³⁺ (Ferric ion) | Yellowish brown |
| AgBr (Silver bromide) | Pale yellow |
🔍 Note: Yellow indicates heavy-metal halides and iron in high oxidation states.
⚫ Black & Brown Compounds
| Compound | Color |
|---|---|
| CuO (Copper(II) oxide) | Black |
| Fe₂O₃ (Ferric oxide) | Brown |
| Ag (Metallic silver) | Grey |
🧠 Exam Tip: Copper Oxide = Black; Ferric = Rust Brown
🌸 Pink and Others
| Compound | Color |
|---|---|
| MnO₂ (Manganese dioxide) | Pink |
| Fe²⁺ (Ferrous ion) | Light green |
🎨 Manganese = Magic Pink, often used in redox reactions.
Table Summary: Common Colored Compounds
| Color | Example Compounds |
|---|---|
| White | AgCl, BaSO₄, PbCl₂, ZnCl₂ |
| Blue | CuSO₄, Cu²⁺ |
| Green | FeSO₄, Ni²⁺, Cr³⁺ |
| Yellow | PbI₂, PbO, Fe³⁺, AgBr |
| Black | CuO |
| Brown | Fe₂O₃ |
| Pink | MnO₂ |
| Grey | Ag (metallic) |
Why This Matters in Exams
These color-based questions are frequently asked in:
- NEET & JEE (Inorganic Chemistry section)
- CBSE Board Practical Viva
- Olympiad and NTSE-level chemistry
Sample NEET MCQ:
What is the color of CuSO₄?
A. Green
B. White
C. Blue ✅
D. Yellow
Memory Tricks for Quick Recall
"Cu and Cr love Green & Blue, Pb and Fe love Yellow too."
"White family: Ba-Zn-Na-K, silent but strong in every way."
Ag Halides:
- AgCl – White
- AgBr – Pale Yellow
- AgI – Yellow (not in image but important)
FAQs on Color of Compounds
Q1. Why are transition metals often colored?
A1. Due to d-d transitions absorbing part of visible light and reflecting the rest.Q2. Why is CuSO₄ blue?
A2. Hydrated Cu²⁺ ions form a crystal structure that absorbs red light and reflects blue.Q3. What makes PbI₂ yellow?
A3. Due to the specific electronic configuration and light absorption properties of lead and iodide.Q4. Are all sulfates white?
A4. Most like BaSO₄ are white, but transition metal sulfates (like CuSO₄) may be colored.
