The difference between the first and second ionization constants of dibasic acids decreases with increase in distance between the carboxyl groups, as shown in the table, is to be explained. Concept introduction: The carboxylate ion obtained by first ionization has one negative charge while the dicarboxylate anion obtained by second ionization has two negative charges. If the two negative charges are in close proximity in the anion, the repulsion between the charges makes the formation of the dianion difficult. In that case there will be a large difference between the first and second ionization constants. With increasing distance between the charges, the mutual repulsion decreases, the dianion becomes relatively stable. This results in small differences between first and second ionization constants. To explain: Why the difference between the first and second ionization constants of dibasic acids, oxalic, succinic and adipic acids, decreases with increase in distance between the carboxyl groups as shown in the table.

Question

The pKa values of a few ortho-, meta-, and para-substituted benzoic acids are shown below: The relative pKa values depend on the substituent. For chloro-substituted benzoic acids, the ortho isomer is the most acidic and the para isomer is the least acidic; for nitro-substituted benzoic acids, the ortho isomer is the most acidic and the meta isomer is the least acidic; and for amino-substituted benzoic acids, the meta isomer is the most acidic and the ortho isomer is the least acidic. Explain these relative acidities. a. Cl: ortho > meta > para b. NO2: ortho > para > meta c. NH2: meta > para > ortho

Answer 1

Question

Chapter 20.SE, Problem 42AP

Interpretation Introduction

Interpretation:

The difference between the first and second ionization constants of dibasic acids decreases with increase in distance between the carboxyl groups, as shown in the table, is to be explained.

Concept introduction:

The carboxylate ion obtained by first ionization has one negative charge while the dicarboxylate anion obtained by second ionization has two negative charges. If the two negative charges are in close proximity in the anion, the repulsion between the charges makes the formation of the dianion difficult. In that case there will be a large difference between the first and second ionization constants. With increasing distance between the charges, the mutual repulsion decreases, the dianion becomes relatively stable. This results in small differences between first and second ionization constants.

To explain:

Why the difference between the first and second ionization constants of dibasic acids, oxalic, succinic and adipic acids, decreases with increase in distance between the carboxyl groups as shown in the table.

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