Evidence in favour of WERNER’S THEORY

1. Electrical Conductance Measurement:

• Molar conductance of a substance depends upon the number of charges on the particle produced by the substance.
• As the number of the particle (i.e. ions) and charges on the coordination sphere increases, molar conductance of the compound increases.
• For example molar conductance for aqueous solution of cobalt(III)chloride complexes with ammonia decreases in the order,

           1.[Co(NH₃)₆]Cl₃ →  [Co(NH₃)₆]³⁺ + 3Cl^–
           2.[Co(NH₃)₅Cl]Cl₂  → [Co(NH₃)₅Cl]²⁺ + 2Cl^–
           3.[Co(NH₃)₄Cl₂]Cl→ [Co(NH₃)₅Cl]⁺+ Cl^–
            4.[Co(NH₃)₃Cl₃]

2.Cryoscopic Measurement:

• The cryoscopic measurement means, measurement of depression in freezing point.
• The depression in freezing point is a colligative property and depends upon the number of particles in the solution. Greater the number of particle more will be the depression in freezing point.
• If a species dissociates into two, three, four…….ions, then depression in freezing point will be two, three, four ……. times respectively.
• Thus the cryoscopic measurement gives the number of ions produced by the dissociation of an ionic compound.

3.Precipitation Reaction:

• The number of ions furnished by a coordination compound can also be determined by precipitation reactions.
• When the complexes CoCl₃.6NH₃,CoCl₃.5NH₃ ,CoCl₃.4NH₃ are treated with an excess of AgNO₃ solution, the number of chloride ion precipitated as AgCl is 3, 2, 1 respectively. This indicates that the number of chloride ion in the ionization sphere is 3, 2, and 1 respectively. The reactions are given below,

          CoCl₃.5NH₃ + 2AgNO₃ → 2AgCl + [Co(NH₃)₅Cl](NO₃)₂

          CoCl₃.4NH₃ + AgNO₃ → AgCl + [Co(NH₃)₄Cl₂](NO₃)

• The structure provided by precipitation reactions is similar to those given by Werner.
• The complex gives no precipitate with the solution. This indicates that all three chloride ion is present in the coordination sphere in this compound.