   Chapter 14, Problem 64E

Chapter
Section
Textbook Problem

# What are the major species present in 0.250 M solutions of each of the following acids? Calculate the pH of each of these solutions.a. HOC6H5b. HCN

(a)

Interpretation Introduction

Interpretation: The major species present in 0.250M solutions of the given acids and the pH value of these solutions 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. A logarithmic scale is used on which, the value 7 corresponds to a neutral species, a value less than 7 corresponds to an acid and a value greater than 7 corresponds to a base.

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

To determine: The major species present in 0.250M solution of C6H5OH and the pH of this solution.

Explanation

Explanation

The major species present in 0.250M solution of C6H5OH are C6H5OH and H2O .

C6H5OH is a weak acid. Hence, it does not completely dissociate in water.

The major species present in the given solution of C6H5OH are C6H5OH and H2O .

The equilibrium constant expression for the stated dissociation reaction is,

Ka=[H+][C6H5O][C6H5OH]

C6H5OH is a comparatively stronger acid than H2O .

The dominant equilibrium reaction for the given case is,

C6H5OH(aq)H+(aq)+C6H5O(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+][C6H5O][C6H5OH] (1)

The [H+] is 6.3×10-6M_ .

The change in concentration of HNO2 is assumed to be x .

The ICE table for the stated reaction is,

C6H5OH(aq)H+(aq)+C6H5O(aq)Inititialconcentration0.25000Changex+x+xEquilibriumconcentration0.250xxx

The equilibrium concentration of [C6H5OH] is (0.250x)M .

The equilibrium concentration of [H+] is xM

(b)

Interpretation Introduction

Interpretation: The major species present in 0.250M solutions of the given acids and the pH value of these solutions 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. A logarithmic scale is used on which, the value 7 corresponds to a neutral species, a value less than 7 corresponds to an acid and a value greater than 7 corresponds to a base.

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

To determine: The major species present in 0.250M solution of HCN and the pH of this solution.

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