
Concept explainers
Approximate the expected voltage for the following
Explain why you get the answers you do.

(a)
Interpretation:
The expected voltage for the given electrochemical reaction is to be calculated by using the molal concentration.
Concept introduction:
Nernst equation is the relation between standard electrode potential and the electrode potential at given conditions of pressures, temperatures and concentrations. Standard electrode potential is the electrode potential at standard temperature, pressure and concentration.
Answer to Problem 8.77E
The expected voltage for the given electrochemical reaction is
Explanation of Solution
The given electrochemical reaction is represented as,
From Table
From Table
The number of electrons transfer in the reaction is
The standard electrical potential of the reaction is calculated as,
Where,
•
•
Substitute the value of the standard electrical of the oxidation half-reaction of zinc-ion and reduction half-reaction of the copper ion in the above equation.
The Nernst equation for the given reaction is represented as,
Where,
•
•
•
•
•
•
•
Substitute the values of
Therefore, the expected voltage for the given electrochemical reaction is
The expected voltage for the given electrochemical reaction is

(b)
Interpretation:
The activity of the given ions is to be calculated. The expected voltage for the given electrochemical reaction is to be calculated by using the activity of ions. The explanation for the value of voltage for the given electrochemical reaction is to be stated.
Concept introduction:
Activity coefficient depends upon the charge and size of the ion, and on the properties of the solvent. Debye-Huckel limiting law, describes the relation between the ionic strength and activity coefficient of a dilute solution.
Answer to Problem 8.77E
The expected voltage for the given electrochemical reaction is
The voltage calculated by the activity of the ions is lower than the voltage calculated by the molal concentration of ions. The value of voltage is more accurate to calculate with activity of individual ions.
Explanation of Solution
The value
At
At
The given electrochemical reaction is represented as,
The standard electrical potential of the reaction is
The ionic strength of the solution is represented as,
Where,
•
•
It is assumed that a monovalent anion in present in the solution. Then the charge on the ion will be
Substitute the value of charges and molality of copper ion and anion in the equation (2).
Substitute the value of charges and molality of zinc ion and anion in the equation (3).
The extended Debye-Huckel equation is shown below,
Where,
•
•
•
•
•
Substitute the value of
Antilog is taken on both side of the above equation.
Substitute the value of
Antilog is taken on both side of the above equation.
The activity of the ion is represented as,
Substitute the value of activity coefficient and molality of copper ion in the equation (5).
Substitute the value of activity coefficient and molality of zinc ion in the equation (5).
The Nernst equation for the given reaction is represented as,
Where,
•
•
•
•
•
•
•
Substitute the value of
The expected voltage for the given electrochemical reaction is
The voltage calculated by the activity of the ions is lower than the voltage calculated by the molal concentration of ions. The value of voltage is more accurate to calculate with activity of individual ions.
The expected voltage for the given electrochemical reaction is
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Chapter 8 Solutions
PHYSICAL CHEMISTRY-STUDENT SOLN.MAN.
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