InterviewSolution
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InterviewSolution
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A solution containing `NH_(4)CI` and `NH_(4)OH` has `[overset(Theta)OH] = 10^(-6) molL^(-1)`, which of the following hydroxides would be precipitated when this solution in added in equal volume to a solution containing `0.1M` of metal ions?A. `Mg(OH)_(2),(K_(sp)=3xx10^(-11))`B. `Fe(OH)_(2)(K_(sp)=8xx10^(-16))`C. `Cd(OH)_(2)(K_(sp)=8xx10^(-6))`D. `AgOH(K_(sp)=5xx10^(-3))` |
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Answer» Correct Answer - B When equal volumes of `(NH_(4)CI + NH_(4)OH)` and metal ions are mixed (volume becomes double and concentration is halved) `:. [overset(Theta)OH] = (10^(-6))/(2), [M^(+n)] = (0.1)/(2)` `Q_(sp) (or IP)` of metal hydroxides of `M(OH)_(2)`type `=[M^(+n)] [overset(Theta)OH]^(2)` `= ((0.1)/(2)) ((10^(-6))/(2))^(2) = (1)/(8) xx 10^(-13)` `= 0.125 xx 10^(-13) = 12.5 xx 10^(-11)` `:. Q_(sp) gt K_(sp) of Mg(OH)_(2) (12.5 xx 10^(-11) gt3 xx 10^(-11))` and `Q_(sp) gt K_(sp)` of `Fe(OH)_(2) (12.5 xx 10^(-11) gt 8 xx 10^(-16))` So both can be precipitated. Since the `k_(sp)` of `Fe(OH)_(2)` is less than `Ksp` of `Mg(OH)_(2)`, so `Fe(OH)_(2)` will be precipiated first. Similarly, `Q_(sp)` (or IP) of metal hydroxides of `M(OH)` type `=[M^(+1)] [overset(Theta)OH] = ((0.1)/(2)) ((10^(-6))/(2))` `= 0.25 xx 10^(-7)` `:.Q_(sp) lt K_(sp) of AgOH (0.25 xx 10^(-7) lt 5 xx10^(-3))` IT can not be precipitated out. Hence `Fe(OH)_(2)` will be precipitated. |
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