Question

In aqueous solution the Ni2" ion forms a complex with four ammonia molecules. Write the formation constant expression for the equilibrium between the hydrated metal ion and the aqueous complex. Under that, write the balanced chemical equation for the first step in the formation of the complex K,=________.

Answer 1

Answer:

The correct equation is "$\frac{[Ni(H_2O)_3 (NH_3)]^{2+}}{[Ni(H_2O)_4]^{2+} [NH_3]}$".

Explanation:

According to the question,

Throughout an aqueous solution, $Ni^{2+}$ exist as $[Ni(H_2O)_4]^{2+}$

So,

⇒ $[Ni(H_2O)_4]^{2+} + 4NH_3 \rightleftharpoons [Ni(NH_3)_4]^{2+} + H_2O$

⇒ $K_f = \frac{[Ni(NH_3)_4]^{2+}}{[Ni(H_2O)_4^{2+}] [NH_3]^4}$

Here, we have excluded $[H_2O]$ as concentration of water will be const.

Now,

This formation of $[Ni(NH_3)_4]^{2+}$ proceeds via several steps,

Step 1:

⇒ $[Ni(H_2O)_4]^{2+}+NH_3 \rightleftharpoons [Ni(H_2O)_3 (NH_3)]^{2+} + H_2O$

⇒ $K_1 = \frac{[Ni(H_2O)_3 (NH_3)]^{2+}}{[Ni(H_2O)_4]^{2+} [NH_3]}$