Question

Among the following the most highly ionized in water is

• A. $C{H}_2(Cl)C{H}_{2}C{H}_{2}COOH$
• B. $C{H}_{3}C{H}_{2}CC{l}_{2}COOH$
• C. $C{H}_{3}CH(Cl)C{H}_{2}COOH$
• D. $C{H}_{3}C{H}_{2}CH(Cl)COOH$

Answer 1

Answer: (B)

lonisation of acid depend upon its strength. A strong acid is easily ionised in water. When an electron withdrawing substituents such as halogen is attached to the carboxylic acid, its acidic strength increases. The inductive effect increases with increase in number of chlorine atoms and it decreases rapidly with distance. Therefore, as the distance between the electron withdrawing group and $-COOH$ group increases, the acidic strength decreases.
Therefore, $C{H}_{3}C{H}_{2}CC{l}_2.COOH$ is the strongest acid in the following given acids , , and . In this acid two chlorine atoms are attached to $-COOH$ group and the distance between chlorine atom and $-COOH$ is minimum.
$C{H}_{3}C{H}_{2}CC{l}_2.COOH$ is the strongest acid. So, it is the most highly ionised in water.