Question

Rank these acids according to their expected pKa values.

ClCH2COOH
ClCH2CH2COOH
CH3CH2COOH
Cl2CHCOOH

In order of highest pka to lowest pka

Answer 1

Concepts and reason

Dissociation constant: Its numerical value which express the degree of dissociation of the substance to its constituted ions. Larger the dissociation constant then dissociation will be faster, thus stronger will be the acid. If the dissociation is slow then dissociation constant will be low and acid will be weak. The is the negative logarithm (base 10) of dissociation constant.

Electronegativity: It’s the tendency of atom involved in covalent bonding to pull the covalent electron towards itself is called as electronegativity.

Inductive effect: Generation of the partial positive and negative charge over the covalent bond due to electronegativity difference of the atoms involved in bonding is called as Inductive effect . The group which have stronger electronegative character is called as

and group which possess electron donating nature is called as group.

Fundamentals

Representative example for dissociation of carboxylic acid was given below

$pKa=-logKa $

It gives the relative strengths of the acids. Stronger acids have smaller values while weak acids have larger values.

The tendency of the atom or group to generate partial negative charge are called effect, while the tendency of the atom or group to donate electron and generate the partial positive charge over it is called as effect.

The representative examples was considered as given below

, then .

The carbon chain with more electronegative atom and lesser number of carbon atoms will have more negative inductive effect , then dissociation is faster.

The carbon chain with less electronegative atom and more number of carbon atoms will have more positive inductive effect , then dissociation is slow.

The correct order of values of the given acids is shown below.

Ans:

The correct order of values of the given acids is shown below.