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</p> Signup and view all the answers

    Which method is NOT used to determine the ionization constant?

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

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

    <p>It slowly decreases</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.</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</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</p> Signup and view all the answers

    Which polyol shows the highest conductivity enhancement?

    <p>Mannitol</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.</p> Signup and view all the answers

    Which hydroxy acid has the highest conductivity enhancement value?

    <p>Glyoxal</p> Signup and view all the answers

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

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

    What is the conductivity enhancement value for glycerol?

    <p>9</p> Signup and view all the answers

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

    <p>Catechol</p> Signup and view all the answers

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

    <p>0</p> Signup and view all the answers

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

    <p>Electron withdrawing groups</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</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.</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.</p> Signup and view all the answers

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

    <p>2.73</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.</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.</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.</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**.</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</p> Signup and view all the answers

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

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

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

    <p>9.25922921</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</p> Signup and view all the answers

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

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

    What role did phenolphthalein play in boric acid analysis?

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

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

    <p>Glyoxal</p> Signup and view all the answers

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

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

    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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    Description

    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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