   Chapter 18, Problem 9RQ

Chapter
Section
Textbook Problem

# What characterizes an electrolytic cell? What is an ampere? When the current applied to an electrolytic cell is multiplied by the time in seconds, what quantity is determined? How is this quantity converted to moles of electrons required? How are moles of electrons required converted to moles of metal plated out? What does plating mean? How do you predict the cathode and the anode half-reactions in an electrolytic cell? Why is the electrolysis of molten salts much easier to predict in terms of what occurs at the anode and cathode than the electrolysis of aqueous dissolved salts? What is overvoltage?

Interpretation Introduction

Interpretation:

The concept of an electrolytic cell and the reactions taking place in an electrolytic cell are to be stated.

Concept introduction:

The non-spontaneous reaction takes place in an electrolytic cell in which there occurs conversion of electrical energy into chemical energy and this is used for the electrolysis of a metal.

To explain: The concept of electrolytic cell; the definition of ampere; the quantity obtained on multiplication of current applied to an electrochemical cell with time in seconds; the conversion of the previously obtained quantity into moles of electrons required; the conversion of moles of electrons required for the moles of metal plated out; the definition of plating; construction of electrolytic cell; electrolysis of molten and aqueous sodium chloride and the definition of the overvoltage.

Explanation

An electrolytic cell is a device that is used for the conversion of electrical energy into chemical energy.

The electrolytic cell converts electrical energy into chemical energy which is a non-spontaneous process. The cell involves the process of electrolysis. Electrolysis involves the process of oxidation-reduction.

When one coulomb of charge flows through a specific point in one second is an ampere.

Ampere is a unit of electrical current that measures the amount of charge flowing per second through a specific point.

When the current applied to an electrolytic cell is multiplied by the time in seconds, it gives the charge passed in the electrolytic cell.

Multiplying current with time gives charge as,

Current×Time=Charge

In this case, current is expressed in ampere (A) , time in seconds (s) and charge in coulomb (C) .

Coulomb can be converted to moles of electron required by multiplying charge with the term (196,485) .

Charge carried by one mole of electrons is 96,485C . Therefore, Coulomb can be converted to moles of electron required by multiplying charge with the term (196,485) .

The moles of electrons required to convert to moles of metal plated out is calculated by the formula,

(1moleofmetalnumberofmolesofelectronsthatarerequiredforreductionofonemoleofnetalion)

The moles of electrons required to convert to moles of metal plated out is calculated by the formula,

(1moleofmetalnumberofmolesofelectronsthatarerequiredforreductionofonemoleofnetalion)

The above relation can be defined by finding the moles of electron transferred and the moles of metal ion produced.

Plating is a method by which the metal surface is covered with a thin layer that increases the life of the metal.

Plating is a method in which the conductive surface of metal is coated with a thin layer. Using plating method, the metal can be modified in the desired way and this also increases the life of the metal.

In an electrolytic cell, anode is positive, while cathode is negative. The oxidation occurs at the anode, while reduction occurs at the cathode.

In an electrolytic cell, the electrons are pushed at the cathode which makes cathode negative and reduction occurs over the cathode. The species having high value of reduction will be reduce at the cathode, while the species with high value of oxidation potential will be oxidized at the anode.

During the electrolysis of molten salt, only one species undergoes oxidation and the other one undergoes reduction. While in the electrolysis of aqueous salt, besides the electrolysis of salt, the electrolysis of water has also to be considered that makes the prediction of the reactions more difficult.

Electrolysis of molten sodium chloride can be expressed by considering the reactions occurring at the cathode and anode.

The reaction at cathode can be expressed as,

Na++e-Na

The reaction at anode can be expressed as,

2Cl-Cl2+2e-

The value of potential for the oxidation of Cl is 1

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