Question

4. A solution of the weak base, ammonia (NH3), was completely neutralized with the strong acid HCl. Write out the dominant equilibrium (including phase labels) that would exist in this "neutralized" solution. HINT: first look at what ions would exist in solution after the non-equilibrium reaction with the strong acid is over. Second, decide if either of these ions is an acid or a base. Lastly, write the equation for this ion acting as an acid or base in water.

Answer 1

Answer:

Predominant equilibrium: $NH_{4}^{+}+H_{2}O\rightleftharpoons NH_{3}+OH^{-}$

Explanation:

Neutralization reaction: $NH_{3}+HCl\rightarrow NH_{4}^{+}+Cl^{-}$

In neutralized solution, $NH_{4}^{+}$ and $Cl^{-}$ ions exist.

We know that $NH_{3}$ is an weak base and HCl is a strong acid.

So, $NH_{4}^{+}$ is a strong conjugate acid of $NH_{3}$  and $Cl^{-}$ is an weak conjugate base of HCl.

Hence, in neutralized solution, $NH_{4}^{+}$ will be predominantly hydrolyzed into $NH_{3}$ and $OH^{-}$.

So, predominant equilibrium: $NH_{4}^{+}+H_{2}O\rightleftharpoons NH_{3}+OH^{-}$