Question

Which of the following acids has the weakest conjugate base?
a. benzoic acid, Ka = 6.31 x 10-5
b. ascorbic acid, pKa = 4.1
c. 3-chlorobenzoic acid, pKa = 3.8
d. chloroacetic acid, Ka = 1.26 x 10-3
e. 2-hydroxybenzoic acid, pKa = 3.0

Answer 1

Answer:

Conjugate base of chloroacetic acid will be weakest.

Explanation:

$K_{a}$ of an acid is a parameter to predict it's acidic strength.

Higher the $K_{a}$, higher will be acid dissociation . Hence acidity will be higher.

We know that the stronger an acid, the weaker it's conjugate base. So higher the $K_{a}$ value of an acid, weaker will be it's conjugate base.

The order of $K_{a}$ value: $(d)(1.26\times 10^{-3})> (e)(10^{-3})> (c)(10^{-3.8})> (b)(10^{-4.1})> (a)(6.31\times 10^{-5})$

So, conjugate base of chloroacetic acid will be weakest.

Answer 2

Acids are the ionic or the molecular substances that donates the proton and are also called Lewis acid. The weakest conjugate base of the acid is chloroacetic acid.

What are conjugate base?

Conjugate bases are the ions or the molecules that gains or accepts the protons from its acid molecule and are represented as $\rm X^{-}$.

The acidic strength of the acid can be estimated by the Ka or the acid dissociation constant. Higher the acid dissociation value higher will be the acidity of the solution or the substance.

Acid and the conjugate base are inversely proportional that is stronger the acidity weaker will be the conjugate base.

The acid dissociation (Ka) value of the chloroacetic acid is the stongest compred to the 2-hydroxybenzoic acid, 3-chlorobenzoic acid, ascorbic acid and benzoic acid.

Therefore, conjugate base of option d. chloroacetic acid will be weakest.

Learn more about conjugate base here:

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