   # In the titration of 50.0 mL of 1.0 M methylamine, CH 3 NH 2 ( K b = 4.4 × 10 −4 ), with 0.50 M HC1, calculate the pH under the following conditions. a. after 50.0 mL of 0.50 M HCl has been added b. at the stoichiometric point ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243

#### Solutions

Chapter
Section ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243
Chapter 14, Problem 66E
Textbook Problem
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## In the titration of 50.0 mL of 1.0 M methylamine, CH3NH2 (Kb = 4.4 × 10−4), with 0.50 M HC1, calculate the pH under the following conditions.a. after 50.0 mL of 0.50 M HCl has been addedb. at the stoichiometric point

(a)

Interpretation Introduction

Interpretation:

The pH under the given conditions is to be calculated.

Concept introduction:

The pH of a solution is define as a figure that expresses the acidity of the alkalinity of a given solution.

The pH of a solution is calculated by the formula, pH=log[H+]

The value of Kw is calculated by the formula,

Kw=KaKb

The relation between pH and pKa is given by Henderson-Hasselbach equation. According to this equation,

pH=pKa+log[Salt][Acid]

### Explanation of Solution

Explanation

To determine: The pH of the given solution after 50.0mL of 0.50M HCl has been added.

Given

The volume of methylamine is 50.0mL .

Molarity of methylamine is 1.0M .

Molarity of HCl is 0.50M .

The reaction that takes place is,

CH3NH2(aq)+HCl(aq)CH3NH3Cl(aq)

The value of Kb for methylamine is 4.4×104 .

The value of Kw is calculated by the formula,

Kw=KaKb=1.0×1014

The value of Ka is calculated by the formula,

Ka=KwKb

Substitute the given value of Kb in the above equation.

Ka=1.0×10144.4×104=2.3×1011

Therefore, the value of Ka is 2.3×1011 .

The stoichiometry of the reaction is represented as,

CH3NH2(aq)+HCl(aq)CH3NH3Cl(aq)Beforereaction0

(b)

Interpretation Introduction

Interpretation:

The pH under the given conditions is to be calculated.

Concept introduction:

The pH of a solution is define as a figure that expresses the acidity of the alkalinity of a given solution.

The pH of a solution is calculated by the formula, pH=log[H+]

The value of Kw is calculated by the formula,

Kw=KaKb

The relation between pH and pKa is given by Henderson-Hasselbach equation. According to this equation,

pH=pKa+log[Salt][Acid]

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