A 35.0-mL sample of 0.150 M acetic acid (CH3COOH) is titrated with 0.150 M NaOH solution. Calculate the pH after the following volumes of base have been added: (c) 34.5 mL, (d) 35.0 mL, (e) 35.5 mL, (f) 50.0 mL.

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780134414232

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Determine the initial moles of acetic acid (CH3COOH) using the formula: \( \text{moles} = \text{volume (L)} \times \text{molarity (M)} \). For a 35.0 mL sample of 0.150 M acetic acid, convert the volume to liters and calculate the moles.

Calculate the moles of NaOH added for each volume given (34.5 mL, 35.0 mL, 35.5 mL, 50.0 mL) using the same formula: \( \text{moles} = \text{volume (L)} \times \text{molarity (M)} \). Convert each volume to liters before calculating.

For each volume of NaOH added, determine the moles of acetic acid and NaOH that react. Since the reaction is 1:1, the moles of NaOH will react with an equal number of moles of acetic acid.

Calculate the moles of acetic acid and acetate ion (CH3COO-) remaining after the reaction for each volume of NaOH added. Use the stoichiometry of the reaction: \( \text{CH}_3\text{COOH} + \text{NaOH} \rightarrow \text{CH}_3\text{COO}^- + \text{H}_2\text{O} \).

Use the Henderson-Hasselbalch equation to calculate the pH for each scenario: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{CH}_3\text{COO}^-]}{[\text{CH}_3\text{COOH}]} \right) \). The \( \text{pK}_a \) of acetic acid is approximately 4.76. Calculate the pH for each volume of NaOH added.

주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Acid-Base Titration

An acid-base titration is a quantitative analytical method used to determine the concentration of an acid or base in a solution. In this process, a solution of known concentration (the titrant) is added to a solution of unknown concentration until the reaction reaches its equivalence point, where the amount of acid equals the amount of base. The pH changes during the titration can be monitored to identify this point.

Buffer Solutions

Buffer solutions are mixtures that can resist changes in pH upon the addition of small amounts of acid or base. In the context of the titration of acetic acid with NaOH, the acetic acid and its conjugate base (acetate ion) form a buffer system that helps maintain a relatively stable pH until the equivalence point is reached. Understanding how buffers work is crucial for calculating pH at various stages of the titration.

pH Calculation

The pH of a solution is a measure of its acidity or basicity, calculated as the negative logarithm of the hydrogen ion concentration. During titration, pH can be calculated using the Henderson-Hasselbalch equation for buffer regions or by using stoichiometry at the equivalence point. After the equivalence point, the pH can be determined based on the concentration of excess hydroxide ions from the added base.