Question

\(\text{NH}_3\) has a \( K_b \) of \( 1.8 \times 10^{-3} \). Which of the following has a \( 5.6 \times 10^{-10} \)?

• A. NH3
• B. NH4+
• C. NH2-
• D. H+

Hint:

Remember, for a base \( B \), the acid dissociation constant \( K_a \) for its conjugate acid can be found using \( K_a \times K_b = K_w \).

Answer 1

The Correct Option is A

Given that \( K_b \) for NH3 is \( 1.8 \times 10^{-3} \), we can calculate its corresponding \( K_a \) for NH4+ using the relationship \( K_a \times K_b = K_w \), where \( K_w = 1 \times 10^{-14} \). This equation connects the acid dissociation constant (\( K_a \)) and the base dissociation constant (\( K_b \)) for conjugate acid-base pairs.

Using the given values, we can calculate \( K_a \) for NH4+ as follows:

\[ K_a = \frac{K_w}{K_b} = \frac{1 \times 10^{-14}}{1.8 \times 10^{-3}} = 5.6 \times 10^{-12} \] This value corresponds to the acid dissociation constant for NH4+, and this is useful in understanding the \( H^+ \) concentration in a solution of NH4+.

Therefore, the correct answer is (a) NH3.