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–
So if we consider all the above equations, we will notice that there is a decreasing order in the number of particles and charges, on the coordination sphere from top to bottom. Therefore molar conductance decreases from top to bottom.
- 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.
- 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.