Question

$N{H}_3$ and $Zn(N{H}_3{)}_4^{2+}$ (assume no partial complexation)

• A. $4.5\times {10}^{-2}M$
• B. $7.5\times {10}^{-2}M$
• C. $32\times {10}^{-2}M$
• D. $9.5\times {10}^{-2}M$

Answer 1

Answer: (A)

$4.5\times {10}^{-2}M$

$\left[Z{n}^{2+}\right]$ final $=1\times {10}^{-4}M$

$\left[Zn\right(N{H}_3{)}_4^{2+}]eq=0.2-{10}^{-4}=0.2$

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

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

$5\times {10}^8=\frac{0.2}{\left({10}^{-4}\right)[N{H}_3{]}^4}$

$(N{H}_3{)}^4=4\times {10}^{-6}=400\times {10}^{-8}$

$\left(N{H}_3\right)=4.5\times {10}^{-2}M$