Question

The correct order of acidic strength is:
A) $HCOOH>C{{H}_{3}}COOH>{{C}_{2}}{{H}_{5}}COOH$
B) ${{C}_{2}}{{H}_{5}}COOH>C{{H}_{3}}COOH>HCOOH$
C) $HCOOH>{{C}_{2}}{{H}_{5}}COOH>C{{H}_{3}}COOH$
D) $C{{H}_{3}}COOH>HCOOH>{{C}_{2}}{{H}_{5}}COOH$

Answer 1

The main concept that leads to the correct answer is that the acidity is dependent on the size of the atom and also the polarity of the hydrogen bond with the other atoms.

Complete step by step answer:
We have studied in our chemistry concepts about the acidity and the basicity of the compounds and the factors which affect these properties.
- Acidity in general means the tendency of a compound that can donate the proton that is the ${{H}^{+}}$ ion.
- This acidity depends mainly on the two factors, that is
(i) Size of the atom
(ii) Polarity of the H-X bond
- The larger the atom is, more is the acidity and also more the polarity of the bond, more will be the acidity.
- In the above given question, we have the aliphatic compound and the acidity of these depends on the inductive effect. If the inductive effect is more, then the acidity decreases and vice-versa.
- Formic acid does not have any electron donating group and hence is more acidic whereas acetic acid has methyl group which is the electron donating group and also propionic acid has more hydrocarbon chain which pushes more electrons towards carboxylic acid group.
Thus, the correct order of acidity of formic acid, ethanoic /acetic acid and propionic acid in the decreasing order is $HCOOH > C{{H}_{3}}COOH > {{C}_{2}}{{H}_{5}}COOH$

So, the correct answer is “Option A”.
$HCOOH > C{{H}_{3}}COOH > {{C}_{2}}{{H}_{5}}COOH$

Note: The main point to be noted is that the acidity does not depend on the number of hydrogen atoms present but on the ease of removal of hydrogen from the compound and do not be confused regarding this fact.