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Ch.17 - Acids and Bases
Tro - Chemistry: A Molecular Approach 5th Edition
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Tutti i libri di testoTro 5th EditionCh.17 - Acids and BasesProblema 143
Capitolo 17, Problema 143

The pH of a 1.00 M solution of urea, a weak organic base, is 7.050. Calculate the Ka of protonated urea.

Guida verificata passo dopo passo
1
Identify that urea is a weak base and its protonated form acts as a weak acid.
Use the given pH to find the concentration of hydrogen ions \([H^+]\) using the formula \([H^+] = 10^{-\text{pH}}\).
Recognize that the concentration of hydrogen ions \([H^+]\) is equal to the concentration of the conjugate base formed \([A^-]\) in the equilibrium reaction.
Set up the expression for the acid dissociation constant \(K_a\) using the formula \(K_a = \frac{[H^+][A^-]}{[HA]}\), where \([HA]\) is the concentration of the protonated urea.
Assume that the initial concentration of protonated urea is approximately 1.00 M, and solve for \(K_a\) using the concentrations found in the previous steps.

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pH and pKa Relationship

pH is a measure of the hydrogen ion concentration in a solution, defined as pH = -log[H+]. The pKa is the negative logarithm of the acid dissociation constant (Ka) and indicates the strength of an acid. For weak bases like urea, the pH can be used to find the pKa of its conjugate acid, which is essential for calculating Ka.
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pH and pOH Calculations

Acid-Base Equilibrium

In acid-base chemistry, equilibrium refers to the state where the rates of the forward and reverse reactions are equal. For protonated urea, the equilibrium can be represented as the dissociation of the conjugate acid into urea and protons. Understanding this equilibrium is crucial for calculating the Ka value, which quantifies the strength of the acid.
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Triprotic Acid Equilibrium

Dissociation Constant (Ka)

The acid dissociation constant (Ka) measures the extent to which an acid can donate protons in solution. A higher Ka value indicates a stronger acid. For protonated urea, calculating Ka involves using the concentrations of the species at equilibrium, which can be derived from the pH of the solution and the initial concentration of urea.
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Characteristics of Ka and Kb
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