The pKa\'s of p-toluic acid and p-tert-butylphenol are 4.2 and 10.2, respectivel
ID: 875432 • Letter: T
Question
The pKa's of p-toluic acid and p-tert-butylphenol are 4.2 and 10.2, respectively.
Based on the pKa's, which of the following is true about the acids?
Check all that apply.
-The Kb of the conjugate base of p-tert-butylphenol is higher than the Kb of the conjugate base of p-toluic acid.
-The conjugate base of p-toluic acid is more stable than the conjugate base of p-tert-butylphenol.
-The conjugate base of p-tert-butylphenol is stronger acid than the conjugate base of p-toluic acid.
-The Ka of p-tert-butylphenol is higher than the Ka of p-toluic acid
-The p-tert-butylphenol is stronger acid than p-toluic acid.
PLEASE HELP!
-The Kb of the conjugate base of p-tert-butylphenol is higher than the Kb of the conjugate base of p-toluic acid.
-The conjugate base of p-toluic acid is more stable than the conjugate base of p-tert-butylphenol.
-The conjugate base of p-tert-butylphenol is stronger acid than the conjugate base of p-toluic acid.
-The Ka of p-tert-butylphenol is higher than the Ka of p-toluic acid
-The p-tert-butylphenol is stronger acid than p-toluic acid.
PLEASE HELP!
Explanation / Answer
Let us find Ka values from the given pKa
The formula used is
pKa = = log Ka
Let's find Ka of p-toluic acid first
4.2 = - log Ka
Ka = 10^-4.2
Ka = 6.31 x 10^-5
Similarly Ka of p-tert-butylphenol would be
10.2 = - log Ka
Ka = 10^-10.2
Ka = 6.31 x 10^-11
Ka of p-toluic acid is 6.31 x 10^-5 and Ka of p-tert-butylphenol is 6.31 x 10^-11
That mean Ka of p-toluic acid is higher than that of p-tert-butylphenol . therefore statement #4 is not correct
The Ka of p-tert-butylphenol is higher than the Ka of p-toluic acid - Not Correct
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Ka values can be directly correlated with the strength of the acid. An acid with higher Ka value is stronger. Based on the Ka values calculated above, we can say that p-toluic acid is stronger than p-tert-butylphenol as it has higher Ka value
Therefore statement #5 is not correct
The p-tert-butylphenol is stronger acid than p-toluic acid - Not Correct
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a relatively stronger acid forms a relatively weaker conjugate base. Now if we compare basicity of the given substances, we can say that p-tertbutylphenol is stronger base than p-toluic acid. Therefore conjugate formed by p-tertbutylphenol would be less acidic than that formed by p-toluic acid.
Also the conjugate of p-toluic acid is more stabilized by resonance so it would be more acidic.
Therefore statement #3 is not correct
The conjugate base of p-tert-butylphenol is stronger acid than the conjugate base of p-toluic acid. - Not Correct
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Since Ka of p-tert-butylphenol is lower, it would have higher Kb . That means conjugate base of p-tert-butylphenol would have higher Kb than conjugate base of p-toluic acid.
Statement #1 is correct
The Kb of the conjugate base of p-tert-butylphenol is higher than the Kb of the conjugate base of p-toluic acid. - Correct
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Conjugate base of p-toluic acid is more stable than that of p-tertbutylphenol. This statement is correct
Statement #2 is correct
The conjugate base of p-toluic acid is more stable than the conjugate base of p-tert-butylphenol.- Correct
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