Quantitative Chemical Analysis
Quantitative Chemical Analysis
9th Edition
ISBN: 9781464135385
Author: Daniel C. Harris
Publisher: W. H. Freeman
Question
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Chapter 17, Problem 17.21P

(a)

Interpretation Introduction

Interpretation:

The current density and overpotential of reduction of azobenzene has to be calculated.

Concept Introduction:

When the electric current is too small, the voltage of cell is given as

E = E(cathode)-E(anode)

E(cathode) is electrode’s potential which is attached to negative terminal of current source.

E(anode) is electrode’s potential which is attached to positive  terminal of current source.

Overpotential: The activation energy of a reaction at an electrode can be overcome by voltage.  The required voltage to apply is called overpotential.

Ohmic potential:  In electrochemical cell, the electrical resistance of a solution while current I flows can be overcome by voltage.  The required voltage to apply is called ohmic potential.

Eohmic=IR

Concentration Polarization:  It is the change in concentration of products and reactants at electrode’s surface unlike they are same in solution.

(a)

Expert Solution
Check Mark

Answer to Problem 17.21P

The overpotential of reduction of azobenzene is 0.85V

Explanation of Solution

To determine: The current density and overpotential of reduction of azobenzene.

The reduction of azobenzene is given as

C6H5N=NC6H5+4H++4e-2C6H5NH2

Electron flow=(4e-sC6H5N=NC6H5)(25.9nmols)(96485C/mol)=1.00×10-2C/s

The current density of reduction of azobenzene is

=1.00×10-2A1.00×10-4m2=100A/m2

For smooth platinum electrode current density of 100A/m2 is equal to 0.85V .

Over potential is 0.85V

(b)

Interpretation Introduction

Interpretation:

The cathode potential at which azobenzene get reduced has to be calculated

Concept Introduction:

When the electric current is too small, the voltage of cell is given as

E = E(cathode)-E(anode)

E(cathode) is electrode’s potential which is attached to negative terminal of current source.

E(anode) is electrode’s potential which is attached to positive  terminal of current source.

Overpotential: The activation energy of a reaction at an electrode can be overcome by voltage.  The required voltage to apply is called overpotential.

Ohmic potential:  In electrochemical cell, the electrical resistance of a solution while current I flows can be overcome by voltage.  The required voltage to apply is called ohmic potential.

Eohmic=IR

Concentration Polarization:  It is the change in concentration of products and reactants at electrode’s surface unlike they are same in solution.

(b)

Expert Solution
Check Mark

Answer to Problem 17.21P

The cathode potential at which azobenzene get reduced is -0.036V

Explanation of Solution

To determine: The cathode potential at which azobenzene get reduced.

UsingNernsteqntheCathodepotentialiscalculatedasE(cathode)  =0.100 -0.05916log[Ti3+]s[TiO2+]s[H+]2=0.100 -0.05916log[0.10][0.050][0.10]2=0.100V-0.136V=-0.036V

(c)

Interpretation Introduction

Interpretation:

The anode potential at which oxygen get reduced to water has to be calculated

Concept Introduction:

When the electric current is too small, the voltage of cell is given as

E = E(cathode)-E(anode)

E(cathode) is electrode’s potential which is attached to negative terminal of current source.

E(anode) is electrode’s potential which is attached to positive  terminal of current source.

Overpotential: The activation energy of a reaction at an electrode can be overcome by voltage.  The required voltage to apply is called overpotential.

Ohmic potential:  In electrochemical cell, the electrical resistance of a solution while current I flows can be overcome by voltage.  The required voltage to apply is called ohmic potential.

Eohmic=IR

Concentration Polarization:  It is the change in concentration of products and reactants at electrode’s surface unlike they are same in solution.

(c)

Expert Solution
Check Mark

Answer to Problem 17.21P

The anode potential at which oxygen get reduced is 1.160V

Explanation of Solution

To determine: The anode potential at which azobenzene get reduced.

UsingNernsteqntheanodepotentialiscalculatedasE(anode)  =1.229 -0.059164log1PO2[H+]4=1.229 -0.059164log1(0.20)(0.10)4=1.229V-0.069V=1.160V

(d)

Interpretation Introduction

Interpretation:

The voltage at which azobenzene reduced to aniline has to be calculated

Concept Introduction:

When the electric current is too small, the voltage of cell is given as

E = E(cathode)-E(anode)

E(cathode) is electrode’s potential which is attached to negative terminal of current source.

E(anode) is electrode’s potential which is attached to positive  terminal of current source.

Overpotential: The activation energy of a reaction at an electrode can be overcome by voltage.  The required voltage to apply is called overpotential.

Ohmic potential:  In electrochemical cell, the electrical resistance of a solution while current I flows can be overcome by voltage.  The required voltage to apply is called ohmic potential.

Eohmic=IR

Concentration Polarization:  It is the change in concentration of products and reactants at electrode’s surface unlike they are same in solution.

(d)

Expert Solution
Check Mark

Answer to Problem 17.21P

The voltage at which azobenzene reduced to aniline is -2.57V

Explanation of Solution

To determine: The voltage at which azobenzene reduced to aniline.

The reduction of azobenzene is given as

C6H5N=NC6H5+4H++4e-2C6H5NH2

E =E(cathode)-E(anode)-IR-Overpotential=-0.036-1.160-(1.00×10-2A)(52.4Ω)-0.85=-2.57V

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