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(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
Colour of Unknown Substances
Chemicals/Ions
Blue
Copper(II), Cu2+
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)
Colour of Unknown Substances
Chemicals/Ions
Brown
I2 (solution)
Lead(IV) oxide, PbO2
Reddish-brown
Iron(III), Fe3+
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
Colour of Unknown Substances
Chemicals/Ions
Green / Light Green
Iron(II), Fe2+
Examples:
Copper(II), Cu2+
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
Colour of Unknown Substances
Chemicals/Ions
Yellow Lead(II) oxide, PbO
Lead(II) iodide, PbI2,
See the web site below for the test for iodidehttp://www.youtube.com/watch?v=tQ_sJTQAnRM
Silver bromide, AgBr(Pale yellow)
Silver iodide, AgI
Colour of Unknown Substances
Chemicals/Ions
Grey Metals (in powder form)
Examples:
Pink Co2+ (hydrated)
Zinc powder
Aluminium powder
Iron powder
Hydrated cobalt(II) chloride crystals, CoCl2.6H2O
Aqueous cobalt(II) chloride solution, CoCl2(aq)
Colour of Unknown Substances
Chemicals/Ions
White Na+, K+, NH4+, Ca2+, Zn2+, Pb2+, Al3+
(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
Ca2+ White residue; carbon dioxide evolved
CaCO3(s) CaO(s) + CO2(g)
white white
Zn2+ Residue is yellow when hot and white when cold; carbon dioxide evolved
ZnCO3(s) ZnO(s) + CO2(g)
white yellow –hot
white - cold
Pb2+ Yellow (orange) residue; carbon dioxide evolved
PbCO3(s) PbO(s) + CO2(g)
white yellow
Al3+ White residue; carbon dioxide evolved
Al2(CO3)3(s) Al2O3(s) + 3CO2(g)
white white
Cu2+ Black residue; carbon dioxide evolved
CuCO3(s) CuO(s) + CO2(g)
green black
Fe2+ 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
Fe3+ Reddish-brown residue; carbon dioxide evolve
Fe2(CO3)3(s) Fe2O3(s) + 3CO2(g)
brown reddish-brown