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?

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=Concentration of productsConcentration of reactants

The value of Kw is calculated by the formula,

Kw=Ka⋅Kb

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=Concentration of productsConcentration of reactants

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=Ka⋅Kb

The value of Ka for HCN is 6.2×10−10 .

The value of Kb is calculated by the formula,

Kb=KwKa

Substitute the value of Ka in the above expression.

Kb=1.0×10−146.2×10−10=1.613×10-5_

The [OH−] is 1.27×10-3 M_ .

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)Inititial concentration0.10000Change−x+x+xEquilibrium concentration0.100−xxx

The equilibrium concentration of [CN−] is (0

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=Concentration of productsConcentration of reactants

The value of Kw is calculated by the formula,

Kw=Ka⋅Kb

To determine: If the given salt is NaC2H3O2 .

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=Concentration of productsConcentration of reactants

The value of Kw is calculated by the formula,

Kw=Ka⋅Kb

To determine: If the given salt is NaF .

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=Concentration of productsConcentration of reactants

The value of Kw is calculated by the formula,

Kw=Ka⋅Kb

To determine: If the given salt is NaCl .

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=Concentration of productsConcentration of reactants

The value of Kw is calculated by the formula,

Kw=Ka⋅Kb

To determine: If the given salt is NaOCl .