Conductivity and Ionization Constants of Ligands

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

How does the ionization constant K** behave with varying ligand concentration?

It decreases with increasing ligand concentration.

It varies with ligand concentration and is independent of boric acid concentration below 0.1M. (correct)

It increases linearly with ligand concentration.

It remains constant regardless of ligand concentration.

What complicates the determination of the ionization constants of boric acid complexes?

Incomplete association between boric acid and the ligand.

Depolymerization of glyoxal and slow decrease in conductivity. (correct)

Changes in temperature during the reaction.

The presence of multiple boric acid forms at high concentrations.

Which method failed to yield clear results in determining the ionization constant?

Half-neutralization method.

Buffer capacity method.

Complexation method.

Conductivity method. (correct)

What is the relationship between the association constant K0 and K1?

K0 represents the interaction of boric acid with glycols, while K1 is the first ionization constant of boric acid. Signup and view all the answers

What effect does glyoxal have on the ionization constant of boric acid?

It contributes to the formation of new acids by association with boric acid. Signup and view all the answers

Which polyol exhibits the highest conductivity as indicated by its value of A?

Mannitol Signup and view all the answers

In the context of conductivity enhancement, which group is primarily suggested to increase conductivity through an inductive effect?

Electron-withdrawing groups Signup and view all the answers

What is the effect of increased functionality on the conductivity as observed in the series of glycerol, erythritol, and sorbitol?

Increases conductivity Signup and view all the answers

Which substance has the lowest dual effects of reactivity and conductivity enhancement due to an inductive effect?

cis-1,2-Cyclohexanediol Signup and view all the answers

How does increased acidity influence conductivity for substances like catechol and α-hydroxy acids?

Increases conductivity due to enhanced properties Signup and view all the answers

What is the relationship between lead tetra-acetate reaction rates and ligand types based on their rates?

There exists a significant 5000-fold difference among them Signup and view all the answers

Which polyol exhibits a conductivity value closest to that of hydroxyl acids?

Catechol Signup and view all the answers

What intrinsic feature is crucial for enhancing conductivity in compounds with hydroxyl groups?

Presence of acidic protons Signup and view all the answers

What does the slope of the corrected data line represent in the context of the glyoxal-boric acid adduct?

The number of moles of glyoxal associated with each mole of borate ion Signup and view all the answers

What is the association constant K derived from the corrected data for glyoxal and borate ion interactions?

4.3 x 10^5 Signup and view all the answers

What effect does the high degree of association between borate ion and glyoxal have on glyoxal concentration during titration?

It reduces glyoxal concentration as titration proceeds Signup and view all the answers

What does the term 'pK**' refer to in the context of the glyoxal-boric acid adduct?

It represents the ionization constant derived from pH measurements Signup and view all the answers

How does the addition of 0.1M potassium chloride affect the data obtained for the glyoxal-boric acid adduct?

It has no significant difference on the gathered data Signup and view all the answers

What is the primary advantage of using the buffer capacity method in this experimental context?

It eliminates the need for glyoxal removal corrections Signup and view all the answers

What is the relationship represented by plotting pK** against the logarithm of the glyoxal concentration?

It allows for the determination of K and n Signup and view all the answers

What does the corrected data achieve concerning the two different concentrations of boric acid in the study?

It brings the results into reasonable agreement Signup and view all the answers

Study Notes

Conductivity of Polyol Ligands

The conductivity of boric acid is significantly enhanced by the presence of polyol ligands.
This enhancement is influenced by several factors:
- Inductive effect: Electron donating groups on the carbons holding the OH groups reduce the enhancement, while electron withdrawing groups increase it.
- Functionality: Increased functionality enhances conductivity, as observed in the series glycerol, erythritol, and sorbitol.
- Acidity: Increased acidity of the ligand enhances conductivity, as seen with catechol and alpha-hydroxy acids.
- These combined effects likely contribute to the enhanced acidity of boric acid by aqueous glyoxal.

Determination of "Ionization Constants"

The "ionization constant" of boric acid complexes is not constant due to varying ratios of boric acid to mono- and di-ligand adducts with changing ligand concentration.
The apparent depolymerization of glyoxal and the slow decrease in conductivity after mixing boric acid and glyoxal further complicate the determination.
"Ionization constants" were determined using:
- Buffer capacity method: This method involved measuring the buffering capacity of the boric acid-glyoxal system as a function of pH.
- Half-neutralization method: This method involved measuring the pH of the half-neutralized glyoxal-boric acid adduct and plotting pK** against the log of the glyoxal concentration.
- Attempts to determine the ionization constant by conductivity methods were unsuccessful.

Results of "Ionization Constant" Determination

The buffer capacity method yielded a more reliable determination of the "ionization constant" due to:
- No correction needed for ligand removal from solution by the borate.
- Glyoxal is more stable at the lower pH used in this method.
The half-neutralization method required corrections for reduced glyoxal concentrations during titration.
Data obtained from both methods indicated that the association constant (K) for the boric acid-glyoxal complex is 4.3 x 10^3.
The number of moles of glyoxal associated with each mole of borate ion (n) was determined to be 3.2.
Addition of potassium chloride did not significantly affect the results.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the role of polyol ligands in enhancing the conductivity of boric acid and the factors affecting ionization constants. Topics include the inductive effect, functionality, and acidity of ligands. Understand the complex behavior of boric acid complexes in varying conditions.