   # Consider a buffered solution containing CH 3 NH 3 Cl and CH 3 NH 2 . Which of the following statements concerning this solution is(are) true? (K a for CH 3 NH 3 + = 2.3 × 10 −11 .) a. A solution consisting of 0.10 M CH 3 NH 3 Cl and 0.10 M CH 3 NH 2 would have a higher buffering capacity than one containing 1.0 M CH 3 NH 3 Cl and 1.0 M CH 3 NH 2 . b. If [CH 3 NH 2 ] &gt; [CH 3 NH 3 + ], then the pH is larger than the pK a value. c. Adding more [CH 3 NH 3 Cl]to the initial buffer solution will decrease the pH. d. If [CH 3 NH 2 ] &lt; [CH 3 NH 3 + ],then pH &lt; 3.36. e. If [CH 3 NH 2 ] = [CH 3 NH 3 + ], then pH = 10.64. ### 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 103CWP
Textbook Problem
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## Consider a buffered solution containing CH3NH3Cl and CH3NH2. Which of the following statements concerning this solution is(are) true? (Ka for CH3NH3+ = 2.3 × 10−11.)a. A solution consisting of 0.10 M CH3NH3Cl and 0.10 M CH3NH2 would have a higher buffering capacity than one containing 1.0 M CH3NH3Cl and 1.0 M CH3NH2.b. If [CH3NH2] > [CH3NH3+], then the pH is larger than the pKa value.c. Adding more [CH3NH3Cl]to the initial buffer solution will decrease the pH.d. If [CH3NH2] < [CH3NH3+],then pH < 3.36.e. If [CH3NH2] = [CH3NH3+], then pH = 10.64.

(a)

Interpretation Introduction

Interpretation: To justify if the given statements are true or false.

Concept introduction: The buffer solution is a solution contains weak acid and conjugate base or weak base and conjugated acid. It resists the change in pH.

To determine: The authenticity of the given statement, “A solution consisting of 0.10MCH3NH3Cl and 0.10MCH3NH2 would have a higher buffering capacity than one containing 1.0MCH3NH3Cl and 1.0MCH3NH2”.

### Explanation of Solution

Explanation

Given

The value of equilibrium constant or acid dissociation constant (Ka) for CH3NH3+ is 2.3×1011.

The given solution is the combination of 0.10MCH3NH3Cl and 0.10MCH3NH2 and containing 1.0MCH3NH3Cl and 1.0MCH3NH2.

The given solution is the combination of acid and their salt. Therefore the pH of such type of solution is calculated by the equation,

pH=pKa+log[salt][acid]

Where,

• pKa is the negative logarithm of dissociation constant.
• [salt] is the concentration of salt.
• [acid] is the concentration of the acid.

The above equation is known as Henderson-Hasselbalch equation.

The pKa that acid dissociation constant is determined by the formula.

pKa=log(Ka)

Substitute the given value of Ka in the above equation.

pKa=log(Ka)=log(2.3×1011)=log(2.3)+11=10.64

Substitute the value of given concentrations in the Henderson equation.

For the combination of 0.10MCH3NH3Cl and 0

(b)

Interpretation Introduction

Interpretation: To justify if the given statements are true or false.

Concept introduction: The buffer solution is a solution contains weak acid and conjugate base or weak base and conjugated acid. It resists the change in pH.

To determine: The authenticity of the given statement, “If [CH3NH2]>[CH3NH3+], then the pH is larger than the pKa value”.

(c)

Interpretation Introduction

Interpretation: To justify if the given statements are true or false.

Concept introduction: The buffer solution is a solution contains weak acid and conjugate base or weak base and conjugated acid. It resists the change in pH.

To determine: The authenticity of the given statement, “Adding more [CH3NH3Cl] to the initial buffer solution will decrease the pH”.

(d)

Interpretation Introduction

Interpretation: To justify if the given statements are true or false.

Concept introduction: The buffer solution is a solution contains weak acid and conjugate base or weak base and conjugated acid. It resists the change in pH.

To determine: The authenticity of the given statement, “If [CH3NH2]<[CH3NH3+] then pH<3.36”.

(e)

Interpretation Introduction

Interpretation: To justify if the given statements are true or false.

Concept introduction: The buffer solution is a solution contains weak acid and conjugate base or weak base and conjugated acid. It resists the change in pH.

To determine: The authenticity of the given statement, “If [CH3NH2]=[CH3NH3+] then pH=10.64”.

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