In a solution total concentration of `M^(3+)` is `2xx10^(-3) (M)` and total concentration of `SCN^(-)` is `1.51xx10^(-3) (M)` and free `SCN^(-)` concentration `= 1xx10^(-5) (M)`
What is the dissociation constant of the complex `M(SCN)^(2+)`?

Options

A. `2xx10^(5)`
B. `2xx10^(-5)`
C. `3.33xx10^(5)`
D. `3.33xx10^(-6)`

Answer

D

Explanation

`underset(50xx10^(-5))(M^(3+))+underset(10-5)(SCN^(-))overset(K_(form))underset(larr)(rarr)underset(150xx10^(-5))(M(SCN)^(2+))`
`K_(form)=(150xx10^(-5))/(50xx10^(-5)xx10^(-5))=3xx105`
`K_(disso)=(1)/(K_(form))=(1)/(3)xx10^(-5)`
`=(10)/(3)xx10^(-6)=3.33xx10^(-5)`