# For propanoic acid (HC 3 H 5 O 2 , K a = 1.3 × 10 −5 ), determine the concentration of all species present, the pH, and the percent dissociation of a 0.100- M solution.

### 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 67E
Textbook Problem
320 views

## For propanoic acid (HC3H5O2, Ka = 1.3 × 10−5), determine the concentration of all species present, the pH, and the percent dissociation of a 0.100-M solution.

Interpretation Introduction

Interpretation: The concentration of all the species present in a 0.100M HC3H5O2 solution, its pH and the percent dissociation 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+]

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

### Explanation of Solution

Explanation

To determine: The concentration of all the species present in a 0.100M HC3H5O2 solution, its pH and the percent dissociation.

The dissociation of HC3H5O2 is, HC3H5O2(aq)  H+(aq) + C3H5O2-(aq)

HC3H5O2 is a weak acid. Hence, it does not completely dissociate in water.

The major species present in the given solution of HC3H5O2 are HC3H5O2 and H2O .

The equilibrium constant expression for the stated dissociation reaction is,

Ka=[H+][C3H5O2][HC3H5O2]

HC3H5O2 is a comparatively stronger acid than H2O .

The dominant equilibrium reaction for the given case is,

HC3H5O2(aq)  H+(aq) + C3H5O2-(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+][C3H5O2][HC3H5O2] (1)

The [H+] and [C3H5O2] is 1.14×10-3M_ .

The change in concentration of HC3H5O2 is assumed to be x .

The ICE table for the stated reaction is,

HC3H5O2(aq)H+(aq)+C3H5O2(aq)Inititialconcentration0.10000Changex+x+xEquilibriumconcentration0.100xxx

The equilibrium concentration of [HC3H5O2] is (0.100x)M .

The equilibrium concentration of [H+] is xM .

The equilibrium concentration of [C3H5O2] is xM

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