# An unknown salt is either NaCN, NaC 2 H 3 O 2 , NaF, NaCl, or NaOCl. When 0.100 mole of the salt is dissolved in 1.00 L of solution, the pH of the solution is 8.07. What is the identity of the salt?

### 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 123E
Textbook Problem
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## An unknown salt is either NaCN, NaC2H3O2, NaF, NaCl, or NaOCl. When 0.100 mole of the salt is dissolved in 1.00 L of solution, the pH of the solution is 8.07. What is the identity of the salt?

(I)

Interpretation Introduction

Interpretation: Identity the given unknown salt is to be determined.

Concept introduction: The pH of a solution is defined as a figure that expresses the acidity of the alkalinity of a given solution.

The pOH of a solution is calculated by the formula, pOH=log[OH]

The sum, pH+pOH=14

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

Ka=ConcentrationofproductsConcentrationofreactants

The value of Kw is calculated by the formula,

Kw=KaKb

### Explanation of Solution

Explanation

To determine: If the given salt is NaCN .

The equilibrium constant expression for the given reaction is, Kb=[HCN][OH][CN]

The dominant equilibrium reaction is,

CN-(aq)HCN(aq)+OH(aq)

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

Kb=ConcentrationofproductsConcentrationofreactants

Where,

• Kb is the base ionization constant.

The equilibrium constant expression for the given reaction is,

Kb=[HCN][OH][CN] (1)

The Kb value is 1.613×10-5_ .

The value, Kw=KaKb

The value of Ka for HCN is 6.2×1010 .

The value of Kb is calculated by the formula,

Kb=KwKa

Substitute the value of Ka in the above expression.

Kb=1.0×10146.2×1010=1.613×10-5_

The [OH] is 1.27×10-3M_ .

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

The liquid components do not affect the value of the rate constant.

The ICE table for the stated reaction is,

CN(aq)HCN(aq)+OH(aq)Inititialconcentration0.10000Changex+x+xEquilibriumconcentration0.100xxx

The equilibrium concentration of [CN] is (0

(II)

Interpretation Introduction

Interpretation: Identity the given unknown salt is to be determined.

Concept introduction: The pH of a solution is defined as a figure that expresses the acidity of the alkalinity of a given solution.

The pOH of a solution is calculated by the formula, pOH=log[OH]

The sum, pH+pOH=14

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

Ka=ConcentrationofproductsConcentrationofreactants

The value of Kw is calculated by the formula,

Kw=KaKb

To determine: If the given salt is NaC2H3O2 .

(III)

Interpretation Introduction

Interpretation: Identity the given unknown salt is to be determined.

Concept introduction: The pH of a solution is defined as a figure that expresses the acidity of the alkalinity of a given solution.

The pOH of a solution is calculated by the formula, pOH=log[OH]

The sum, pH+pOH=14

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

Ka=ConcentrationofproductsConcentrationofreactants

The value of Kw is calculated by the formula,

Kw=KaKb

To determine: If the given salt is NaF .

(IV)

Interpretation Introduction

Interpretation: Identity the given unknown salt is to be determined.

Concept introduction: The pH of a solution is defined as a figure that expresses the acidity of the alkalinity of a given solution.

The pOH of a solution is calculated by the formula, pOH=log[OH]

The sum, pH+pOH=14

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

Ka=ConcentrationofproductsConcentrationofreactants

The value of Kw is calculated by the formula,

Kw=KaKb

To determine: If the given salt is NaCl .

(V)

Interpretation Introduction

Interpretation: Identity the given unknown salt is to be determined.

Concept introduction: The pH of a solution is defined as a figure that expresses the acidity of the alkalinity of a given solution.

The pOH of a solution is calculated by the formula, pOH=log[OH]

The sum, pH+pOH=14

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

Ka=ConcentrationofproductsConcentrationofreactants

The value of Kw is calculated by the formula,

Kw=KaKb

To determine: If the given salt is NaOCl .

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