# Calculate the percent dissociation of the acid in each of the following solutions. a. 0.50 M acetic acid b. 0.050 M acetic acid c. 0.0050 M acetic acid d. Use Le Châtelier’s principle to explain why percent dissociation increases as the concentration of a weak acid decreases. e. Even though the percent dissociation increases from solutions a to c, the [H + ] decreases. Explain.

### Chemistry: An Atoms First Approach

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

Chapter
Section

### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243
Chapter 13, Problem 73E
Textbook Problem
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## Calculate the percent dissociation of the acid in each of the following solutions.a. 0.50 M acetic acidb. 0.050 M acetic acidc. 0.0050 M acetic acidd. Use Le Châtelier’s principle to explain why percent dissociation increases as the concentration of a weak acid decreases.e. Even though the percent dissociation increases from solutions a to c, the [H+] decreases. Explain.

(a)

Interpretation Introduction

Interpretation: The percent dissociation of the acid in each of the given solutions is to be calculated.

Concept introduction: At equilibrium, the equilibrium constant expression is expressed by the formula,

Ka=ConcentrationofproductsConcentrationofreactants

The percent dissociation of an acid is calculated by the formula,

Percentdissociation=Equilibriumconcentrationof[H+]Initialconcentrationoftheacid×100

To determine: The percent dissociation for a 0.50M solution of acetic acid (CH3COOH) .

### Explanation of Solution

Explanation

The equilibrium constant expression for the given reaction is, Ka=[H+][CH3COO][CH3COOH]

CH3COOH is a comparatively stronger acid than H2O .

The dominant equilibrium reaction for the given case is,

CH3COOH(aq)H+(aq)+CH3COO(aq)

At equilibrium, the equilibrium constant expression is expressed by the formula,

Ka=ConcentrationofproductsConcentrationofreactants

Where,

• Ka is the acid dissociation constant.

The equilibrium constant expression for the given reaction is,

Ka=[H+][CH3COO][CH3COOH] (1)

The [H+] is 3.0×10-3M_ .

The change in concentration of CH3COOH is assumed to be x .

The ICE table for the stated reaction is,

CH3COOH(aq)H+(aq)+CH3COO(aq)Inititialconcentration0.5000ChangexxxEquilibriumconcentration0.50xxx

The equilibrium concentration of [CH3COOH] is (0.50x)M .

The equilibrium concentration of [H+] is xM .

The equilibrium concentration of [CH3COO] is xM .

The Ka for CH3COOH is 1.8×105 .

Substitute the value of Ka , [CH3COOH] , [H+] and [CH3COO] in equation (1)

(b)

Interpretation Introduction

Interpretation: The percent dissociation of the acid in each of the given solutions is to be calculated.

Concept introduction: At equilibrium, the equilibrium constant expression is expressed by the formula,

Ka=ConcentrationofproductsConcentrationofreactants

The percent dissociation of an acid is calculated by the formula,

Percentdissociation=Equilibriumconcentrationof[H+]Initialconcentrationoftheacid×100

To determine: The percent dissociation for a 0.050M solution of acetic acid (CH3COOH) .

(c)

Interpretation Introduction

Interpretation: The percent dissociation of the acid in each of the given solutions is to be calculated.

Concept introduction: At equilibrium, the equilibrium constant expression is expressed by the formula,

Ka=ConcentrationofproductsConcentrationofreactants

The percent dissociation of an acid is calculated by the formula,

Percentdissociation=Equilibriumconcentrationof[H+]Initialconcentrationoftheacid×100

To determine: The percent dissociation for a 0.0050M solution of acetic acid (CH3COOH) .

(d)

Interpretation Introduction

Interpretation: The percent dissociation of the acid in each of the given solutions is to be calculated.

Concept introduction: At equilibrium, the equilibrium constant expression is expressed by the formula,

Ka=ConcentrationofproductsConcentrationofreactants

The percent dissociation of an acid is calculated by the formula,

Percentdissociation=Equilibriumconcentrationof[H+]Initialconcentrationoftheacid×100

To determine: An explanation for the increase in percent dissociation with a decrease in the concentration of a weak acid, on the basis of Le Chatelier’s principle.

(e)

Interpretation Introduction

Interpretation: The percent dissociation of the acid in each of the given solutions is to be calculated.

Concept introduction: At equilibrium, the equilibrium constant expression is expressed by the formula,

Ka=ConcentrationofproductsConcentrationofreactants

The percent dissociation of an acid is calculated by the formula,

Percentdissociation=Equilibriumconcentrationof[H+]Initialconcentrationoftheacid×100

To determine: An explanation for the decrease in [H+] even though the percent dissociation increases.

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