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.