Question

What is the ratio of uncomplexed to complexed $Z{n}^{2+}$ ion in a solution that is 10M in $N{H}_3$, if the stability constant of $\left[Zn\right(N{H}_3{)}_4{]}^{2+}$ is $3\times {10}^9$?

• A. $3.3\times {10}^{-9}$
• B. $3.3\times {10}^{-11}$
• C. $3.3\times {10}^{-14}$
• D. $3\times {10}^{-13}$

Answer 1

Answer: (C)

$3.3\times {10}^{-14}$

$Z{n}^{2+}+4N{H}_3\rightleftharpoons \left[Zn\right(N{H}_3{)}_4{]}^{2+}$

$K_f=\frac{\left[Zn\right(N{H}_3{)}_4{]}^{2+}}{\left[Z{n}^{2+}\right][N{H}_3{]}^4}$$=3\times {10}^9$

$\therefore \frac{\left[Zn\right(N{H}_3{)}_4{]}^{2+}}{\left[Z{n}^{2+}\right][10{]}^4}=3\times {10}^9$

$\frac{\left[Zn\right(N{H}_3{)}_4{]}^{2+}}{\left[Z{n}^{2+}\right]}$$=3\times {10}^{13}$

$\frac{Z{n}^{2+}}{\left[Zn\right(N{H}_3{)}_4{]}^{2+}}$$=3.3\times {10}^{-14}$