Question

question 21 of 32 the acid dissociation constant, ( k_a ), of ( \text{hno}_3 ) is ( 4.0 \times 10^{-4} ). what does the ( k_a ) value indicate about this compound?

a. ( \text{hno}_3 ) is a strong acid.

b. ( \text{hno}_3 ) is a strong base.

c. ( \text{hno}_3 ) is a weak acid.

d. ( \text{hno}_3 ) is neither an acid nor a base.

Explanation:

1. Recall the concept of acid dissociation constant (\(K_a\)): A large \(K_a\) (usually \(K_a>1\)) means a strong acid (completely dissociates), a small \(K_a\) ( \(K_a < 1\)) means a weak acid (partially dissociates).
2. Analyze the given \(K_a = 4.0\times10^{-4}\), which is less than 1. So \(HNO_3\) does not dissociate completely, indicating it is a weak acid.
3. Eliminate other options: \(HNO_3\) has an acid dissociation constant, so it is an acid (eliminate B and D). Since \(K_a\) is small, it is not a strong acid (eliminate A).

Answer:

C. \( \ce{HNO_3} \) is a weak acid.