Question

Write formula of the following coordination compounds:
(x) Tetraammine diaqua cobalt (III) chloride
(y) Potassium trioxalato chromate (III)

Hint:

Name $\Rightarrow$ formula: determine ligand charges and count, assign oxidation state from the Roman numeral, find the net charge on the complex, then add the required counter-ions.

Answer 1

(x) Tetraammine diaqua cobalt (III) chloride
Ligands: 4 ammine (NH$_3$; neutral) and 2 aqua (H$_2$O; neutral). Central metal: Co(III) $\Rightarrow$ complex cation charge $= +3$. Chloride is the counter anion ($-1$ each), hence three Cl$^-$ are required.
[2pt] \[ \boxed{\text{[Co(NH}_3\text{)}_4(\text{H}_2\text{O})_2]\text{Cl}_3}} \] (y) Potassium trioxalato chromate (III)
Oxalato (oxalate) ligand = C$_2$O$_4^{2-}$ (bidentate). Three such ligands: total charge $= -6$. Central metal: Cr(III) $\Rightarrow$ complex-anion charge $= (+3) + (-6) = -3$. Balance with three K$^+$.
[2pt] \[ \boxed{\text{K}_3[\text{Cr}(\text{C}_2\text{O}_4)_3]} \]