To find the pH of an ammonium acetate solution, we use the fact that ammonium acetate is a salt resulting from the neutralization of a weak acid (acetic acid, $CH_3COOH$) by a weak base (ammonium hydroxide, $NH_4OH$). The respective ionization constant values for the weak acid $K_a$ and the weak base $K_b$ are given as $1.8 \times 10^{-5}$.

Firstly, calculate the $pK_a$ and $pK_b$ values.

• $pK_a = -\log(K_a) = -\log(1.8 \times 10^{-5})$
• $pK_b = -\log(K_b) = -\log(1.8 \times 10^{-5})$

Given that the values of $K_a$ and $K_b$ are the same, their $pK_a$ and $pK_b$ values will also be the same, establishing a neutral condition where the effects of the acid and base neutralize each other.

The formula used to determine the pH of a solution of such a salt is:

$$pH = \frac{1}{2}(pK_w + pK_a - pK_b)$$

Where $pK_w$ is the ionic product of water, which is 14 at 25°C. In this specific case, since $pK_a = pK_b$, the formula simplifies to:

$$pH = \frac{1}{2}(14 + pK_a - pK_a)$$

$$pH = \frac{1}{2}(14)$$

$$pH = 7$$

The pH of an ammonium acetate solution in this scenario is 7, indicating a neutral solution.