Analytical chemistry is the branch of Chemistry where we detect the presence of ions.
After completion of this chapter don’t forget to complete the Practice Set(CLICK)
List of cations and anions forming colourless salts.
| Cations | Anions |
| NH4+, Na+, K+, Ca2+, Mg2+, Al3+, Pb2+, Zn2+ | CO32-, HCO3–, SO42-, Cl–, CH3COO–, Br–, O2_, NO3–, HSO3–, HSO4–, S2-, SO32-, PO43- |
Cations forming coloured salts
| Cation | Solid | Solution |
| Cu2+ | Blue | Blue |
| Fe2+ | Light green | Light green |
| Fe3+ | Yellow to brown | Yellow |
| Ni2+ | Green | Green |
| Cr3+ | Bluish green to violet | Bluish green |
| Mn2+ | Light pink | Light pink |
| Co2+ | Violet to pink | Pink |
Anions forming coloured salts
| Anion | Solid | Solution |
| CrO42- | Yellow | Yellow |
| Cr2O72- | Orange | Orange |
| MnO4– | Purple with greenish lustre | Purple |
| MnO42- | Purple | Purple |
Colour of some important compounds
| Compound | Colour |
| PbS, HgS, Ag2S, FeS, CoS, NiS, FeO, Fe2O3, MnO2, CoO, NiO, CuS, PbO2 | Black |
| HgO, HgI2, Pb3O4, Cu2O | Red |
| FeCl3, CdS, PbO, AgI | Yellow |
| Ca(OH)2, Mg(OH)2 | White |
| Zn(OH)2, Al(OH)3 | Gelatinous White |
| Pb(OH)2 | Chalky white |
| Fe(OH)2 | Dirty green |
| Fe(OH)3 | Reddish brown |
| Cu(OH)2 | Pale blue |
| Na2ZnO2, Na2PbO2 | Colourless solution |
| | |
Action of NaOH solution
| Salt | Reaction | Colour of the ppt. | Effect of excess NaOH on the ppt. |
| Ca2+ | CaCl2 + 2NaOH → Ca(OH)2 ↓+ 2NaCl | White | Insoluble |
| Zn2+ | ZnCl2 + 2NaOH → Zn(OH)2 ↓+ 2NaCl Zn(OH)2 + 2NaOH → Na2ZnO2 + 2H2O | Gelatinous White | Colourless solution |
| Pb2+ | Pb(NO3)2 + 2NaOH → Pb(OH)2 ↓ + 2NaNO3 Pb(OH)2 + 2NaOH → Na2PbO2 + 2H2O | Chalky White | Colourless solution |
| Fe2+ | FeSO4 + 2NaOH → Fe(OH)2 ↓+ Na2SO4 | Dirty green | Insoluble |
| Fe3+ | FeCl3 + 3NaOH → Fe(OH)3 ↓+ 3NaCl | Reddish brown | Insoluble |
| Cu2+ | CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4 | Pale Blue | Insoluble |
Action of NH4OH solution
| Salt | Reaction | Colour of the ppt. | Effect of excess NaOH solution on the ppt. |
| Ca2+ | – | – | – |
| Zn2+ | ZnCl2 + 2 NH4OH → Zn(OH)2 ↓+ 2 NH4Cl Zn(OH)2 + (NH4)2SO4 + 2 NH4OH → [Zn(NH3)4]SO4+ 4H2O Tetrammine zinc sulphate | Gelatinous White | Colourless Solution |
| Pb2+ | Pb(NO3)2 + 2 NH4OH → Pb(OH)2 ↓ + 2 NH4NO3 | Chalky White | Insoluble |
| Fe2+ | FeSO4 + 2 NH4OH → Fe(OH)2 ↓+ (NH4)2SO4 | Dirty green | Insoluble |
| Fe3+ | FeCl3 + 3 NH4OH → Fe(OH)3 ↓+ 3 NH4Cl | Reddish brown | Insoluble |
| Cu2+ | CuSO4 + 2 NH4OH → Cu(OH)2 + (NH4)2SO4 Cu(OH)2 + (NH4)2SO4 + 2 NH4OH → [Cu(NH3)4]SO4+ 4H2O Tetrammine copper sulphate | Pale Blue | Inky blue solution |
For complete Detection of the ions you may also visit: Test for Cation
