Glyoxal and Boric Acid Reaction Study
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Questions and Answers

Which factor does NOT affect the ionization constant of boric acid complexes?

  • The concentration of glyoxal
  • The concentration of boric acid
  • The temperature of the solution (correct)
  • The ratio of boric acid to ligand adducts

What effect does glyoxal have on boric acid according to the content?

  • It forms a stable complex with boric acid.
  • It has no effect on its ionization.
  • It promotes its ionization. (correct)
  • It decreases its ionization.

What does the ionization constant, K**, depend on?

  • The volume of the solution
  • The concentration of the ligand (correct)
  • The initial concentration of boric acid
  • The temperature of the solution

What is the reported conductivity increment for a solution containing glyoxal and boric acid?

<p>1032 n-mhos (D)</p> Signup and view all the answers

Which method is NOT used to determine the ionization constant?

<p>Spectrophotometric method (D)</p> Signup and view all the answers

What is the association constant of glyoxal with borate ion as mentioned in the content?

<p>2.0 x 10^5 (A)</p> Signup and view all the answers

What happens to the conductivity after mixing boric acid and glyoxal?

<p>It slowly decreases (B)</p> Signup and view all the answers

What is suggested about the reaction preference of glyoxal regarding boric acid and borate ion?

<p>Glyoxal reacts preferentially with borate ion. (C)</p> Signup and view all the answers

What does the equation provided for ionization constants include?

<p>An association constant and a first ionization constant (A)</p> Signup and view all the answers

Which of the following factors was unexpectedly affected by the presence of borax in aqueous glyoxal solutions?

<p>Acidity of the solution (D)</p> Signup and view all the answers

Which polyol shows the highest conductivity enhancement?

<p>Mannitol (C)</p> Signup and view all the answers

What role do electron donating groups have on the carbon holding the OH groups in terms of conductivity enhancement?

<p>They reduce conductivity enhancement. (B)</p> Signup and view all the answers

Which hydroxy acid has the highest conductivity enhancement value?

<p>Glyoxal (B)</p> Signup and view all the answers

Among the following, which factor is noted to enhance conductivity?

<p>Increased acidity (B)</p> Signup and view all the answers

What is the conductivity enhancement value for glycerol?

<p>9 (A)</p> Signup and view all the answers

Which of the following polyols has a conductivity enhancement value closest to 500?

<p>Catechol (C)</p> Signup and view all the answers

What is the conductivity enhancement value of cis-1,2-cyclohexanediol?

<p>0 (D)</p> Signup and view all the answers

Which element or group is observed to increase conductivity enhancement the most?

<p>Electron withdrawing groups (C)</p> Signup and view all the answers

What is the association constant, K, obtained in the absence of salt?

<p>2.8 x 10^5 (D)</p> Signup and view all the answers

What effect does the presence of salt have on the precision of pH readings?

<p>It increases the precision of the readings. (C)</p> Signup and view all the answers

What does the slope of the line obtained from plotting pK** against the negative logarithm of the glyoxal concentration indicate?

<p>The number of glyoxal molecules associated with each boric acid molecule. (C)</p> Signup and view all the answers

What was the value of n obtained from the given experiment?

<p>2.73 (D)</p> Signup and view all the answers

What correction was applied to the pK** value in the absence of salt?

<p>A correction of about 0.2 to 0.4 percent was applied. (C)</p> Signup and view all the answers

What is the significance of diluting the solution with potassium chloride?

<p>It increases the value of K to 3.6 x 10^5. (A)</p> Signup and view all the answers

Which method is indicated for determining the dissociation constant in the absence of salt?

<p>Back titration after adding acid. (C)</p> Signup and view all the answers

In the experiment described, what is the primary variable measured in relation to the pH?

<p>The half-neutralization point pK**. (B)</p> Signup and view all the answers

What was the method used to determine the ionization constants of boric acid?

<p>Titration with sodium hydroxide (D)</p> Signup and view all the answers

Which factor interferes with the buffer capacity method for boric acid?

<p>Interference of carbon dioxide (B)</p> Signup and view all the answers

What happens to the dissociation constant of boric acid when salts like KCl are added?

<p>It accentuates the point of minimum buffer capacity (B)</p> Signup and view all the answers

What value of pK for boric acid ionization was obtained through the experiments?

<p>9.25922921 (B)</p> Signup and view all the answers

What is the significance of thermodynamic equilibrium constants in the context provided?

<p>They are obtained by extrapolating data to zero ionic strength (B)</p> Signup and view all the answers

What conductivity value was measured for 0.5M boric acid before purification?

<p>38.5 u-mhos (D)</p> Signup and view all the answers

What role did phenolphthalein play in boric acid analysis?

<p>It served as a pH indicator (D)</p> Signup and view all the answers

What effect does standing time have on the conductivity of the boric acid-glyoxal solution?

<p>It decreases conductivity significantly (B)</p> Signup and view all the answers

What was the primary reason for the negative conductivity increment observed with glutaraldehyde and a-hydroxyadipaldehyde?

<p>The free acid in the aldehydes decreased boric acid ionization. (C)</p> Signup and view all the answers

Which aldehyde has a greater affinity for cellulose compared to glutaraldehyde and a-hydroxyadipaldehyde?

<p>Glyoxal (B)</p> Signup and view all the answers

What method was used to determine ionization constants in the study?

<p>Differential potentiometric method (D)</p> Signup and view all the answers

Which factor decreases the contribution of boric acid to the conductivity in the mixture?

<p>Presence of free acid in the aldehydes (B)</p> Signup and view all the answers

What did the method of Kili’ primarily minimize during the determination of ionization constants?

<p>Disturbance in equilibria (A)</p> Signup and view all the answers

In the given equation for calculating minimum buffer capacity, what does K l * represent?

<p>The ionization constant (D)</p> Signup and view all the answers

What does a plot of incremental change in pH versus the increment of acid or base added illustrate?

<p>The maximum pH change denoted by d@H) (B)</p> Signup and view all the answers

Which concentration of boric acid was used in the experiment for determining ionization constants?

<p>0.2 M (D)</p> Signup and view all the answers

Flashcards

Glyoxal's effect on boric acid

Glyoxal promotes the ionization of boric acid by removing borate ions from solution.

Glyoxal-borate association

Glyoxal forms an association with borate ions, indicated by an association constant of 2.8 x 10^3.

Conductivity increment

The conductivity of a solution containing glyoxal and boric acid is unusually high, reaching 1032 n-mhos.

Polycyclic structure of glyoxal

The data confirm the polycyclic structure of aqueous glyoxal.

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Varying ionization constants

Different methods for determining ionization constants of glyoxal-borate mixtures yield different results.

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Ionization Constant of Boric Acid Complexes

The ionization constant of boric acid complexes changes with the ligand (like boric acid and glycol) concentration because the ionizing species changes as the ratio of boric acid to its adducts changes with varying ligand concentrations. This complexity also involves the glyoxal depolymerization and conductivity decrease after mixing.

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Variable Ionization Constant (K**)

The ionization constant (K**) of boric acid-glycol acids depends on the ligand concentration (C1) but not the boric acid concentration (below 0.1M).

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Determination Methods for Ionization Constants

Ionization constants are determined by two methods: buffer capacity and half-neutralization/approximate EMF techniques. Conductivity methods were not reliable.

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Buffer Capacity Method

A technique used to determine ‘ionization constants’ for the given systems. It's used to analyze the change in pH under a particular range of additions of a buffer solution and the resulting effect on the acidity.

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Association Constant (K1)

K1 is the constant relating to the association or combination of boric acid and another chemical species (often a glycol).

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Conductivity Enhancement

Increased ability of a substance to conduct electricity, influenced by factors like ligand structure and acidity.

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Inductive Effect

Electron-donating groups reduce conductivity enhancement, while electron-withdrawing groups increase it.

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Functionality

Increased number of reactive groups (e.g., -OH) in a molecule leads to higher conductivity.

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Acidity

Higher acidity of a compound enhances conductivity enhancement in a chemical reaction.

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Ligands

Molecules that can bond to a central atom or ion and affect conductivity.

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Polyol effect

Increased functionality enhances conductivity in a reaction.

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Lead tetra-acetate reaction

A reaction that shows various rates of reaction with ligands.

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Cyclic Intermediate

A temporary molecule formed in a reaction that has a ring-like structure.

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K*

The association constant representing the equilibrium between glyoxal and boric acid in solution. It reflects the strength of the interaction between them.

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n

The number of glyoxal molecules associated with a single boric acid molecule in the complex formed. Represents the stoichiometry of their interaction.

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What is the effect of salt on the association constant K*?

The presence of salt, like potassium chloride, increases the value of K*. This indicates that salt enhances the interaction between glyoxal and boric acid.

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How does the value of n change with the addition of salt?

The addition of salt leads to a slight decrease in the value of n. This suggests that salt might influence the relative proportions of glyoxal and boric acid in the formed complex.

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What is the typical effect of salt on the pH measurements?

Salt reduces polarization of the electrodes used for pH measurement, leading to more precise readings.

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Why is the ionic strength of the solution important?

Thermodynamic equilibrium constants are best determined in solutions with minimal ionic strength. The ionic strength of a solution affects the activity of ions, which influences the equilibrium.

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How does the buffer capacity method affect ionic strength?

The buffer capacity method, used to determine dissociation constants, requires an initial addition of acid, leading to an increase in ionic strength compared to solutions of boric acid and hydronium ions alone.

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Why is the correction for the pK** value small?

The correction needed due to the increased ionic strength is less than 0.4%, indicating a minimal impact on the overall pK** value.

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Boric Acid Ionization

The process where boric acid releases a hydrogen ion (H+) in solution, becoming a negatively charged borate ion (B(OH)4-)

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Glyoxal's Influence

Glyoxal increases boric acid's ionization by forming a complex with borate ions, pulling them out of solution and making more H+ available

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Buffer Capacity

The ability of a solution to resist changes in pH when an acid or base is added

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Salt's Effect on Ionization

Adding salts like KCl or NaCl increases the ionization of weak acids, making them release more H+

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Thermodynamic Constant

The true ionization constant of a compound, measured under ideal conditions with no interfering factors

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Ionic Strength

A measure of the total concentration of ions in a solution

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Debye-Hückel Equation

A mathematical formula used to predict the behavior of electrolyte solutions by relating ionic strength to conductivity

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Boric Acid Purification

Recrystallization of boric acid to remove impurities, usually done by dissolving and then cooling to form crystals

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Glutaraldehyde's effect on boric acid

Glutaraldehyde, when added to boric acid, does not increase the acidity of the boric acid. This indicates that glutaraldehyde does not form a complex with boric acid.

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Glyoxal's affinity for cellulose

Glyoxal has a stronger attraction to cellulose compared to glutaraldehyde or a-hydroxyadipaldehyde. This means glyoxal binds more readily to cellulose.

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Glyoxal's hydration

Glyoxal forms a strong bond (hydrates) with water molecules.

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Minimum buffer capacity method

This method determines ionization constants by measuring the smallest change in pH when adding acid or base to a solution. This approach minimizes disturbances in the solution's equilibrium.

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Buffer capacity equation

The buffer capacity is calculated using the equation: " =V’iJ[AW),] where AV is the volume of base added, B is the concentration of the base, V is the total volume, and dH is the change in pH.

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Ionization constant (K**)

This value represents the strength of an acid in a solution. It is calculated through successive approximations using the buffer capacity equation.

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Conductivity increment in glyoxal-borate mixtures

The conductivity of a solution containing glyoxal and boric acid is unusually high, reaching 1032 n-mhos.

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Conductivity increment in glutaraldehyde-borate mixtures

Glutaraldehyde, when added to boric acid, causes a decrease in conductivity, indicating that it reduces the ionization of the boric acid.

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Study Notes

Reaction of Glyoxal with Boric Acid and Borate Ion

  • Glyoxal promotes the ionization of boric acid, likely by withdrawing borate ions from solution.
  • The association constant between glyoxal and borate ion is 2.8 x 105.
  • Conductivity in glyoxal and boric acid solutions is unusually high (1032 µ-mhos).
  • This supports the polycyclic structure of aqueous glyoxal.
  • Glyoxal-borate salts were not isolated.
  • Different methods for determining ionization "constants" yielded different results, potentially due to glyoxal's preference for reacting with borate ions over boric acid.
  • "Constants" corresponded to molar ratios of glyoxal to borate ion of 3-2 and 2-7 at 25°C.
  • The latter ratio likely represents the average degree of glyoxal polymerization in solution.

Discussion

  • Glyoxal, known to exist in hydrated form, primarily reacts as a dialdehyde.
  • The discovery that borax increases the acidity of aqueous glyoxal solutions was unexpected.
  • Increased acidity in boric acid solutions often results from reactions with bidentate ligands (e.g., polyhydric alcohols, phenols, hydroxy acids, and dibasic acids).
  • This often involves a coordination reaction with the conjugate base of boric acid, B(OH)4- in water.
  • In the glyoxal-boric acid system, the cis configuration and planar OC-CO conformation of glyoxal enhance boric acid acidity.
  • Electron donating and withdrawing groups on the carbons holding hydroxyl groups affect the conductivity enhancement.
  • Increased functionality and acidity also contribute to greater conductivity enhancement.

Determination of Conductivity Increment

  • Glyoxal's increase in boric acid solution conductivity stems from complex formation.
  • Conductivity initially increases, but then decreases after about 6 hours due likely to polymerization changes in glyoxal during dilution.
  • When a stock solution of 5.73M glyoxal is mixed with a stock solution of boric acid at 25°C to 0.500M, the conductivity increment is 1642 µ-mhos initially, but decreases to 1032 µ-mhos after 64 hours.

Determination of "Ionization Constants"

  • Ionization constants aren't constant because the ratio of components changes with concentration, altering the ionizing species.
  • This is further complicated by glyoxal's slow depolymerisation.
  • Ionization constants often follow a formula, K** = CK1K2 + K1, where K1 is the association constant between boric acid and glycol, and K1 is the first ionization constant of boric acid.
  • Ionization constants were measured using the buffer capacity method and the half-neutralization method.
  • Conductivity-based methods weren't reliable for measuring these constants due to the complexes forming with glyoxal.

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Reaction Of Glyoxal With Boric Acid And Borate Ion PDF

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Explore the fascinating reaction between glyoxal and boric acid, highlighting the ionization of boric acid and the unusual conductivity levels in their solutions. This quiz delves into aspects such as the association constant between glyoxal and borate ions, ionic behavior, and polycyclic structures in aqueous solutions.

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