MHT CET Medical202624 April 2026Evening ShiftChemistryCoordination CompoundsActual
Why aqueous cobalt chloride solution when treated with conc. HCl develops a deep blue colored solution?
Options
- ADue to formation of [ CoCl ₄]²⁺ having tetrahedral geometry.
- BDue to formation of [ CoCl ₄]²⁻ having tetrahedral geometry.
- CDue to formation of [ CoCl ₄]²⁻ having octahedral geometry.
- DDue to formation of [ CoCl ₄]²⁺ having octahedral geometry.
Correct answer
B. Due to formation of [ CoCl ₄]²⁻ having tetrahedral geometry.
Step-by-step solution
Aqueous cobalt chloride solution contains the pink-colored octahedral complex [ Co ( H ₂ O )₆]²⁺ . When concentrated HCl is added, the chloride ions act as ligands and replace the water molecules in the coordination sphere. The reaction is given by: [ Co ( H ₂ O )₆]²⁺ + 4 Cl ^- [ CoCl ₄]²⁻ + 6 H ₂ O The complex [ CoCl ₄]²⁻ has a coordination number of 4 . Since Cl ^- is a weak field ligand, the complex undergoes sp^3 hybridization, resulting in a tetrahedral geometry. The formation of this tetrahedral [ CoCl ₄]²⁻ c