Question

The strongest acid is
a.) Acetic acid
b.) Trichloroacetic acid
c.) Dichloroacetic acid
d.) Monochloroacetic acid

Answer 1

Negative inductive effect can be shown by the halogen, when the halogens gets attached with the alkyl group, they tend to induce the $- I$ effect or negative induction, while creating $+ I$ effect or positive induction, on the alkyl group.

Complete step by step answer:
- There are different definitions of acids, by considering the easiest one, which states that “acids are those substances which tend to loss proton i.e. ${H^ + }$ ions”. Now in the above question, whoever tends to lose ${H^ + }$ ion faster is the strongest acid.
- Since each of the four variants of acetic acid are attached with the same halogen atoms, we need to see the effect of the halogen atom on the acid.
- Now we know that halogen has an inductive effect when it is added to any hydrocarbon, which creates a negative inductive effect by pulling its electron known as $- I$.
- When halogen is attached to acid it pulls the electron density from the alkyl group, making itself $\delta -$ , therefore alkyl group gets electron deficit and pulls the electron from oxygen of $O - H$ bond, resulting in the oxygen to get less electronegative, which in turn pulls the electron from hydrogen resulting in the release of ${H^ + }$ ion.
Therefore, the greater the number of halogen attached to the acid, the stronger the acid is.
- Now comparing our option we can conclude that:
$CC{l_3}COOH > CHC{l_2}COOH > C{H_2}ClCOOH > C{H_3}COOH$
The correct answer is option “B” .

Note: If there is an inductive effect by the attaching of an electronegative element on the molecule than you should consider that greater the number of the electronegative element more the polarizing power of that molecule.