(A) Colour of Substances
The several possibilities for a particular colour are given below:
Colour of Unknown Chemicals/Ions
Substances
Copper(II) oxide, CuO
Iron(II) oxide, FeO
Black
Manganese(IV) oxide, MnO2
Iodine crystals, I2

Colour of Unknown Chemicals/Ions
Substances
Examples:
Hydrated copper(II)
sulfate crystals,
CuSO4.5H2O
Aqueous copper(II)
sulfate solution,
CuSO4(aq)
Blue
Copper(II), Cu2+
Hydrated copper(II)
nitrate crystals,
Cu(NO3)2.3H2O
Aqueous copper(II)
nitrate solution,
Cu(NO3)2(aq)
Anhydrous cobalt(II) chloride, CoCl2

Colour of Unknown Chemicals/Ions
Substances
I2 (solution)
Brown
Lead(IV) oxide,
PbO2
Examples:
Hydrated iron(III)
nitrate crystals,
Fe(NO3)3.9H2O
Iron(III), Fe3+
Aqueous iron(III)
nitrate solution,
Reddish-brown Fe(NO3)3(aq)
Iron(III) oxide,
Fe2O3
Copper metal

Colour of Unknown Chemicals/Ions
Substances
Examples:
Hydrated iron(II)
sulfate crystals,
FeSO4.7H2O
Iron(II), Fe2+
Green / Light
Green Aqueous iron(II)
sulfate solution,
FeSO4(aq)
Examples:
Copper(II)
carbonate, CuCO3
Copper(II), Cu2+
Hydrated
copper(II) chloride
crystals,
CuCl2.2H2O
Potassium
Purple manganate(VII),
KMnO4
Potassium
Orange dichromate(VI),
K2Cr2O7

Colour of Unknown Chemicals/Ions
Substances
Lead(II)
Yellow 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

Colour of Unknown Chemicals/Ions
Substances
Examples:
Zinc powder
Metals (in
Grey powder form) Aluminium powder
Iron powder
Co2+ Hydrated cobalt(II)
Pink (hydrated) chloride crystals,
CoCl2.6H2O
Aqueous cobalt(II)
chloride solution,
CoCl2(aq)

Colour of Unknown Chemicals/Ions
Substances
Na+, K+, NH4+, Ca2+, Zn2+, Pb2+, Al3+
White
(Absence of salts like iron(II), iron(III), copper(II) and other
transition elements)
Colourless Dilute acids, alkalis, hydrogen peroxide(H2O2)
Solution
(B) Action of Heat on Carbonates
Cation Observations/Gas Equation
evolved
Na+ White residue; Na2CO3.10H2O(s) → Na2CO3(s) + 10H2O(g)
Water vapour evolved white crystals white powder
+
K White residue Not decomposed
Ca 2+
White residue; carbon CaCO3(s) → CaO(s) + CO2(g)
dioxide evolved
white white
Zn2+ Residue is yellow when hot ZnCO3(s) → ZnO(s) + CO2(g)
and white when cold;
white yellow –hot
carbon dioxide evolved
white - cold
Pb 2+
Yellow (orange) residue; PbCO3(s) → PbO(s) + CO2(g)
carbon dioxide evolved
white yellow
Al3+ White residue; carbon Al2(CO3)3(s) → Al2O3(s) + 3CO2(g)
dioxide evolved
white white
Cu 2+
Black residue; carbon CuCO3(s) → CuO(s) + CO2(g)
dioxide evolved
green black
Fe2+ Black residue turning FeCO3(s) → FeO(s) + CO2(g)
reddish brown on contact
green black
with air (oxidation); carbon
dioxide evolved
4FeO(s) + O2(g) → 2Fe2O3(s)
air reddish-brown
Fe3+ Reddish-brown residue; Fe2(CO3)3(s) → Fe2O3(s) + 3CO2(g)
carbon dioxide evolve
brown reddish-brown