Colour Of Substances

1. (A) Colour of Substances
The several possibilities for a particular colour are given below:
Colour of Unknown
Substances
Chemicals/Ions

Black
Copper(II) oxide, CuO
Iron(II) oxide, FeO
Manganese(IV) oxide, MnO2
Iodine crystals, I2

2. Colour of Unknown
Substances
Chemicals/Ions
Blue
Copper(II), Cu
2+
Examples:
Anhydrous cobalt(II) chloride, CoCl2
Hydrated copper(II)
sulfate crystals,
CuSO4.5H2O
Aqueous copper(II)
sulfate solution,
CuSO4(aq)
Hydrated copper(II)
nitrate crystals,
Cu(NO3)2.3H2O
Aqueous copper(II)
nitrate solution,
Cu(NO3)2(aq)

3. Colour of Unknown
Substances
Chemicals/Ions
Brown
I2 (solution)
Lead(IV) oxide,
PbO2
Reddish-brown
Iron(III), Fe
3+
Examples:
Copper metal
Hydrated iron(III)
nitrate crystals,
Fe(NO3)3.9H2O
Aqueous iron(III)
nitrate solution,
Fe(NO3)3(aq)
Iron(III) oxide,
Fe2O3

4. Colour of Unknown
Substances
Chemicals/Ions
Green / Light
Green
Iron(II), Fe
2+
Examples:
Copper(II), Cu
2+
Examples:
Purple
Potassium
manganate(VII),
KMnO4
Orange
Potassium
dichromate(VI),
K2Cr2O7
Hydrated iron(II)
sulfate crystals,
FeSO4.7H2O
Aqueous iron(II)
sulfate solution,
FeSO4(aq)
Copper(II)
carbonate, CuCO3
Hydrated
copper(II) chloride
crystals,
CuCl2.2H2O

5. Colour of Unknown
Substances
Chemicals/Ions
Yellow
Lead(II)
oxide,
PbO
Lead(II)
iodide,
PbI2,
See the web site below for the test for iodide
http://www.youtube.com/watch?v=tQ_sJTQAnRM
Silver
bromide,
AgBr
(Pale
yellow)
Silver
iodide, AgI

6. Colour of Unknown
Substances
Chemicals/Ions
Grey
Metals (in
powder form)
Examples:
Pink
Co
2+
(hydrated)
Zinc powder
Aluminium powder
Iron powder
Hydrated cobalt(II)
chloride crystals,
CoCl2.6H2O
Aqueous cobalt(II)
chloride solution,
CoCl2(aq)

7. Colour of Unknown
Substances
Chemicals/Ions
White
Na
+
, K
+
, NH4
+
, Ca
2+
, Zn
2+
, Pb
2+
, Al
3+

(Absence of salts like iron(II), iron(III), copper(II) and other
transition elements)
Colourless
Solution
Dilute acids, alkalis, hydrogen peroxide(H2O2)
(B) Action of Heat on Carbonates
Cation Observations/Gas
evolved
Equation
Na
+
White residue;
Water vapour evolved
Na2CO3.10H2O(s) ® Na2CO3(s) + 10H2O(g)
white crystals white powder
K
+
White residue Not decomposed
Ca
2+
White residue; carbon
dioxide evolved
CaCO3(s) ® CaO(s) + CO2(g)
white white
Zn
2+
Residue is yellow when hot
and white when cold;
carbon dioxide evolved
ZnCO3(s) ® ZnO(s) + CO2(g)
white yellow –hot
white - cold
Pb
2+
Yellow (orange) residue;
carbon dioxide evolved
PbCO3(s) ® PbO(s) + CO2(g)
white yellow
Al
3+
White residue; carbon
dioxide evolved
Al2(CO3)3(s) ® Al2O3(s) + 3CO2(g)
white white
Cu
2+
Black residue; carbon
dioxide evolved
CuCO3(s) ® CuO(s) + CO2(g)
green black
Fe
2+
Black residue turning
reddish brown on contact
with air (oxidation); carbon
dioxide evolved
FeCO3(s) ® FeO(s) + CO2(g)
green black
4FeO(s) + O2(g) ® 2Fe2O3(s)
air reddish-brown
Fe
3+
Reddish-brown residue;
carbon dioxide evolve
Fe2(CO3)3(s) ® Fe2O3(s) + 3CO2(g)
brown reddish-brown