Write the conditions of colour of transition metal ion. Write the alloy used in Fischer Tropsch process.

Answer:

Conditions for a transition metal ion to be coloured:

1. The ion must have an incompletely filled (partly filled) d subshell, i.e. unpaired d electrons (d¹ to d⁹). Ions with d⁰ (Sc³⁺, Ti⁴⁺) or d¹⁰ (Zn²⁺, Cu⁺) configuration are colourless.
2. The ligands around the ion must split the d orbitals into sets of different energy, so that d–d transitions are possible.
3. The energy difference between the split d levels must correspond to light of the visible region; the ion absorbs some wavelengths and shows the complementary colour (e.g. [Ti(H₂O)₆]³⁺ is purple).

Alloy used in Fischer–Tropsch process: cobalt–thorium (Co–Th) alloy, used as the catalyst for the synthesis of gasoline (hydrocarbons) from CO and H₂.