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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 34
17장, 문제 34

Solve an equilibrium problem (using an ICE table) to calculate the pH of each solution. a. 0.18 M CH3NH2 b. 0.18 M CH3NH3Cl c. a mixture that is 0.18 M in CH3NH2 and 0.18 M in CH3NH3Cl

검증된 단계별 안내
1
Identify the species in solution and their roles: CH3NH2 is a weak base, and CH3NH3Cl is a salt that can provide CH3NH3+, the conjugate acid of CH3NH2.
For part (a), set up an ICE table for the equilibrium: CH3NH2 + H2O ⇌ CH3NH3+ + OH-. Use the initial concentration of CH3NH2 (0.18 M) and assume initial concentrations of CH3NH3+ and OH- are 0. Define the change in concentration as -x for CH3NH2 and +x for both CH3NH3+ and OH-.
Write the expression for the base dissociation constant (Kb) of CH3NH2: Kb = [CH3NH3+][OH-] / [CH3NH2]. Substitute the equilibrium concentrations from the ICE table into this expression.
For part (b), recognize that CH3NH3Cl dissociates completely in water to give CH3NH3+ and Cl-. Set up an ICE table for the equilibrium: CH3NH3+ + H2O ⇌ CH3NH2 + H3O+. Use the initial concentration of CH3NH3+ (0.18 M) and assume initial concentrations of CH3NH2 and H3O+ are 0. Define the change in concentration as -x for CH3NH3+ and +x for both CH3NH2 and H3O+.
For part (c), recognize that the solution is a buffer containing both CH3NH2 and CH3NH3+. Use the Henderson-Hasselbalch equation: pH = pKa + log([base]/[acid]). Calculate pKa from the known Kb of CH3NH2 and the relation pKa + pKb = 14. Substitute the concentrations of CH3NH2 and CH3NH3+ into the equation to find the pH.

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주요 개념

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

Equilibrium and ICE Tables

Equilibrium in chemistry refers to the state where the concentrations of reactants and products remain constant over time. An ICE table (Initial, Change, Equilibrium) is a tool used to organize the concentrations of species involved in a reaction at different stages. It helps in calculating the changes in concentration as the system reaches equilibrium, which is essential for determining pH in acid-base reactions.
추천 영상:
가이드 코스
01:14
ICE Charts and Equilibrium Amount

Acid-Base Chemistry

Acid-base chemistry involves the study of substances that can donate protons (acids) or accept protons (bases). In this question, CH3NH2 (methylamine) is a weak base, while CH3NH3Cl (methylammonium chloride) is its conjugate acid. Understanding the strength of these acids and bases, as well as their dissociation in water, is crucial for calculating the pH of the solutions.
추천 영상:
가이드 코스
02:00
Arrhenius Acids and Bases

pH Calculation

pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration. For weak acids and bases, the pH can be calculated using the equilibrium concentrations derived from the ICE table. In mixtures of weak acids and their conjugate bases, the Henderson-Hasselbalch equation can also be applied to find the pH, highlighting the relationship between pH, pKa, and the concentrations of the acid and base.
추천 영상:
가이드 코스
02:15
pH Calculation Example
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