Question

question 20 (1 point)
polyprotic acids have multiple $k_{\text{a}}$ values. what statement best describes this?

$\bigcirc$ the first $k_{\text{a}}$ is most significant.
$\bigcirc$ all the $k_{\text{a}}$ values are significant for accuracy.
$\bigcirc$ only the first two are significant.
$\bigcirc$ the first is generally very small and they get progressively bigger, as protons become harder to remove.

you can use this periodic table and reference table of acid and base ionization constants during the quiz. however, as stated in the course outline, and in the orientation session, this quiz is not open book. you cannot access course material work as a group, use a

Explanation:

For polyprotic acids, when considering their \(K_a\) values (acid dissociation constants), the first \(K_a\) (for the first proton dissociation) is the most significant in many cases. This is because the first proton is typically the easiest to remove (due to electrostatic and structural factors), and subsequent protons are harder to remove (so their \(K_a\) values are smaller and less impactful on the overall acidity in most common analytical or chemical contexts). The statement "All the \(K_a\) values are significant for accuracy" is incorrect because often only the first (or sometimes first few) matter significantly for practical calculations. "Only the first two are significant" is also incorrect as it's not a general rule that only two matter. The statement "The first is generally very small and they get progressively bigger, as protons become harder to remove" is wrong because as protons become harder to remove, \(K_a\) values get smaller (since \(K_a\) is related to the ease of dissociation; smaller \(K_a\) means weaker acid strength for that dissociation step). So the best description is that the first \(K_a\) is most significant.

Answer:

The first \(K_{\text{a}}\) is most significant.