Which of the following complexes will lead to lowest cryoscopic measurement ?

Options

A. `CoCI_(3)` . `6NH_(3)`
B. `CoCI_(3)` . `5NH_(3)`
C. `CoCI_(3)` . `4NH_(3)`
D. `CoCI_(3)` . `3NH_(3)`

Answer

A

Explanation

The freezin point of a liquid is lowered when a chemical substance is dissolved in it . Cryoscopic measuring how much the freezing point is lowered. The depression of freezing point obtained depends on the number of particles present i.e., more the particles, the higer the depression . cryoscopic measurements can be used to find if a given substance dissociates into two ion it will give twice the expected depression for a single particle . If three ions are formed this will give three times expected depression . Thus:
`[Co(NH_(3))_(6)]C1_(3) rarr 4` particles (6 charges)
`[Co(NH_(3))_(5)C1]C1_(2) rarr 3` particles (4 charges)
`[Co(NH_(3))_(4)C1_(2)]C1 rarr 2` particles (2 charges)
`[Co(NH_(3))_(3)C1_(3)] rarr 1` particle (0 charges)
The number of particles formed form a complex determines the magnitude of the depression of freezing point . Note that the number of particles formed may be different from the number of charges which can obtained form conductivity measurements . the two types of information can be used to establish the structure .