Use the Henderson–Hasselbalch equation to calculate the pH of each solution in Problem 29.

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Identify the components of the buffer solution from Problem 29, which typically includes a weak acid and its conjugate base.

Write down the Henderson–Hasselbalch equation: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where \([\text{A}^-]\) is the concentration of the conjugate base and \([\text{HA}]\) is the concentration of the weak acid.

Determine the \(\text{pK}_a\) of the weak acid from a table of acid dissociation constants or from the problem statement.

Substitute the concentrations of the conjugate base \([\text{A}^-]\) and the weak acid \([\text{HA}]\) into the Henderson–Hasselbalch equation.

Calculate the logarithmic term and add it to the \(\text{pK}_a\) to find the pH of the solution.

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주요 개념

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Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. It relates the pH of the solution to the pKa of the acid and the ratio of the concentrations of the conjugate base to the acid. The equation is expressed as pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the base and [HA] is the concentration of the acid.

Buffer Solutions

Buffer solutions are mixtures that can resist changes in pH upon the addition of small amounts of acids or bases. They typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid. Understanding how buffers work is essential for applying the Henderson-Hasselbalch equation, as it helps predict how the pH will change in response to different concentrations of the acid and base.

pKa and Acid-Base Strength

The pKa is a measure of the strength of an acid in solution; it is the negative logarithm of the acid dissociation constant (Ka). A lower pKa value indicates a stronger acid, which dissociates more completely in solution. Knowing the pKa of the acid involved in the buffer system is crucial for using the Henderson-Hasselbalch equation effectively, as it directly influences the calculated pH.