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Ch.17 - Aqueous Ionic Equilibrium
Tro - Chemistry: A Molecular Approach 4th Edition
Tro4th EditionChemistry: A Molecular ApproachISBN: 9780134112831당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Tro 4th EditionCh.17 - Aqueous Ionic Equilibrium문제 73b
17장, 문제 73b

Consider the titration of a 25.0-mL sample of 0.175 M CH3NH2 with 0.150 M HBr. Determine each quantity: b. the volume of added acid required to reach the equivalence point, d. the pH at one-half of the equivalence point, f. the pH after adding 5.0 mL of acid beyond the equivalence point.

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b. Volume of added acid required to reach the equivalence point:
1. Write the balanced chemical equation for the reaction: \( \text{CH}_3\text{NH}_2 + \text{HBr} \rightarrow \text{CH}_3\text{NH}_3^+ + \text{Br}^- \).
2. Calculate the moles of \( \text{CH}_3\text{NH}_2 \) in the initial solution: \( \text{moles} = \text{volume (L)} \times \text{molarity} \).
3. Use the stoichiometry of the reaction to determine the moles of \( \text{HBr} \) needed, which is equal to the moles of \( \text{CH}_3\text{NH}_2 \) since the reaction is 1:1.
4. Calculate the volume of \( \text{HBr} \) solution required using its molarity: \( \text{volume (L)} = \frac{\text{moles of HBr}}{\text{molarity of HBr}} \).
d. pH at one-half of the equivalence point:
1. At one-half of the equivalence point, the concentration of \( \text{CH}_3\text{NH}_2 \) equals the concentration of \( \text{CH}_3\text{NH}_3^+ \).
2. Use the Henderson-Hasselbalch equation: \( \text{pH} = \text{pK}_a + \log\left(\frac{[\text{base}]}{[\text{acid}]}\right) \).
3. Since \([\text{base}] = [\text{acid}]\), \( \log\left(\frac{[\text{base}]}{[\text{acid}]}\right) = 0 \), so \( \text{pH} = \text{pK}_a \).
4. Calculate \( \text{pK}_a \) from \( \text{pK}_w = 14 \) and \( \text{pK}_b \) of \( \text{CH}_3\text{NH}_2 \): \( \text{pK}_a = 14 - \text{pK}_b \).
f. pH after adding 5.0 mL of acid beyond the equivalence point:
1. Calculate the total volume of \( \text{HBr} \) added: \( \text{volume at equivalence point} + 5.0 \text{ mL} \).
2. Determine the moles of excess \( \text{HBr} \) added beyond the equivalence point.
3. Calculate the concentration of excess \( \text{H}^+ \) ions in the total solution volume.
4. Use the concentration of \( \text{H}^+ \) to find the pH: \( \text{pH} = -\log[\text{H}^+] \).

주요 개념

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

Titration and Equivalence Point

Titration is a quantitative analytical method used to determine the concentration of a solute in a solution. The equivalence point occurs when the amount of titrant added is stoichiometrically equivalent to the amount of substance in the sample. In this case, it is where the moles of HBr added equal the moles of CH3NH2 present, allowing for the calculation of the volume of acid needed.
추천 영상:
가이드 코스
03:06
Equivalence Point in Titration

pH and Buffer Solutions

pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration. At one-half of the equivalence point in a titration of a weak base with a strong acid, the solution acts as a buffer, where the concentrations of the weak base and its conjugate acid are equal, resulting in a pH that can be calculated using the pKa of the weak base.
추천 영상:
가이드 코스
03:02
Buffer Solutions

Post-Equivalence Point pH

After the equivalence point in a titration, the solution contains excess strong acid, which significantly influences the pH. The pH can be calculated by determining the concentration of the excess HBr in the solution after adding a specific volume of acid beyond the equivalence point. This results in a lower pH, reflecting the increased acidity of the solution.
추천 영상:
가이드 코스
07:28
pH at the Equivalence Point Example
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