(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