The first $pK_a$ of malonic acid is lower than the $pK_a$ of acetic acid while its second $pK_a$ is higher than the $pK_a$ of acetic acid.
The first $pK_a$ of malonic acid is higher than the $pK_a$ of acetic acid while its second $pK_a$ is lower than the $pK_a$ of acetic acid.
Both the first and the second $pK_a$ of malonic acid are lower than the $pK_a$ of acetic acid.
Both the first and the second $pK_a$ of malonic acid are higher than the $pK_a$ of acetic acid.
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The Correct Option isA
Solution and Explanation
To determine the correct statement about the \(pK_a\) values of malonic acid and acetic acid, let's break down the information:
Malonic acid is a dicarboxylic acid that can dissociate in two steps:
The first dissociation of malonic acid (removal of the first proton) is given a \(pK_a1\) value.
The second dissociation (removal of the second proton) is given a \(pK_a2\) value.
Acetic acid is a monocarboxylic acid and has only one \(pK_a\) value for its dissociation.
Typical \(pK_a\) values are as follows:
Acetic acid: \(pK_a \approx 4.76\)
Malonic acid:
\(pK_a1 \approx 2.83\)
\(pK_a2 \approx 5.69\)
Comparison:
The first \(pK_a\) of malonic acid (2.83) is indeed lower than the \(pK_a\) of acetic acid (4.76), meaning malonic acid can donate a proton more easily than acetic acid in the first dissociation.
The second \(pK_a\) of malonic acid (5.69) is higher than the \(pK_a\) of acetic acid (4.76), indicating that after losing one proton, malonic acid holds onto the second proton more tightly than acetic acid holds onto its single proton.
Based on this analysis, the correct statement is:
"The first \(pK_a\) of malonic acid is lower than the \(pK_a\) of acetic acid while its second \(pK_a\) is higher than the \(pK_a\) of acetic acid."
Therefore, the correct answer is:
The first \(pK_a\) of malonic acid is lower than the \(pK_a\) of acetic acid while its second \(pK_a\) is higher than the \(pK_a\) of acetic acid.
