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Ch.16 - Acid-Base Equilibria
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoBrown 14th EditionCh.16 - Acid-Base EquilibriaProblema 112
Capitolo 16, Problema 112

The following observations are made about a diprotic acid H2A: (i) A 0.10 M solution of H2A has pH = 3.30. (ii) A 0.10 M solution of the salt NaHA is acidic. Which of the following could be the value of pKa2 for H2A: (i) 3.22, (ii) 5.30, (iii) 7.47, or (iv) 9.82?

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1
Determine the concentration of hydrogen ions [H^+] in the 0.10 M solution of H2A using the pH value: \([H^+] = 10^{-pH}\).
Use the concentration of [H^+] to find the ionization constant \(K_{a1}\) for the first ionization of H2A: \(H_2A \rightleftharpoons H^+ + HA^-\).
Recognize that the solution of NaHA is acidic, indicating that the second ionization \(HA^- \rightleftharpoons H^+ + A^{2-}\) is significant, and \(K_{a2}\) must be considered.
Compare the given pKa values to determine which one is consistent with the observed acidity of the NaHA solution, knowing that a lower pKa indicates a stronger acid.
Select the pKa value that is consistent with the acidic nature of the NaHA solution, considering that \(pKa_2\) should be higher than \(pKa_1\) but still low enough to contribute to the acidity.

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Diprotic Acids

Diprotic acids are acids that can donate two protons (H⁺ ions) per molecule in a solution. They undergo two dissociation steps, each characterized by its own acid dissociation constant (Ka). Understanding the behavior of diprotic acids is crucial for predicting their pH and the resulting equilibrium in solution.
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3 forms of Diprotic Acids

pH and pKa Relationship

The pH of a solution is a measure of its acidity, defined as the negative logarithm of the hydrogen ion concentration. The pKa is the negative logarithm of the acid dissociation constant (Ka) and indicates the strength of an acid; lower pKa values correspond to stronger acids. The relationship between pH and pKa helps determine the degree of ionization of the acid in solution.
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pH and pOH Calculations

Salt Hydrolysis

When a salt of a weak acid is dissolved in water, it can undergo hydrolysis, affecting the pH of the solution. In this case, NaHA, the salt of the weak acid H2A, can release H⁺ ions, making the solution acidic. Understanding how salts interact with water is essential for predicting the pH of solutions containing weak acids and their salts.
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Ionic Salts
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