Chapter 25, Problem 25.1QAP

Interpretation Introduction

(a)

Interpretation:

The voltammetry and amperometry needs to be differentiated.

Concept introduction:

In voltammetry, the current in the electrode is usually measured with the help of a three-electrode system. In this system, a constant or varying potential is applied at the surface of the electrode whereas the process of amperometry generally involves a current that is measured as a function of independent variable which can either be time or the electrode potential.

Answer to Problem 25.1QAP

Voltammetry involves the current in any cell being calculated in terms of applied potential. This potential is measured in the conditions that encourage the polarization of an indicator or the electrode.

In amperometry, the current in the cell is evaluated or determined at a fixed voltage.

Explanation of Solution

In amperometry, the current is measured as a function of time or electrode potential. This type of variable is independent. In voltammetry, a constant or varying potential is applied at the surface of the electrode. This method is only suitable when there are small amounts of the analyte being consumed at the surface of the electrode.

Interpretation Introduction

(b)

Interpretation:

The linear scan and pulse voltammetry needs to be differentiated.

Concept introduction:

Linear scan voltammetry is a method in which current at the working electrode is measured while the potential is swept linearly with the time whereas in pulse voltammetry, a series of voltage pulses are superimposed on the potential linear sweep.

Answer to Problem 25.1QAP

Linear scan voltammetry involves the measurement of the current as the applied potential increases with time. In pulse voltammetry, current is estimated at that moment when the difference between faradic curve and the interfering charging current is enormous or huge.

Explanation of Solution

Pulse voltammetry is a type of method that is used to make the measurements related to the electrochemistry, with a series of voltage pulses which are then superimposed over the potential linear sweep.

Linear scan voltammetry is a type of method in which the current at the working electrode is first measured, with the potential being swept linearly with time.

Interpretation Introduction

(c)

Interpretation:

The differential pulseand square wave voltammetry needs to be differentiated.

Concept introduction:

The method of square wave voltammetry makes use of the combined square waves as well as the potential of the staircase, which is applied to the electrodes and is stationary. Differential pulse voltammetry is a method that is usually used for the electrochemical measurements with a series of regulate voltage pulses which are then superimposed on stairsteps.

Answer to Problem 25.1QAP

The difference between the differential pulse voltammetry and square wave voltammetry is that the differential pulse voltammetry makes use of the pulses which are differential whereas square wave voltammetry makes use of the waves which havea square wave form.

Explanation of Solution

Square wave voltammetry is a method in which the potential is applied on the stationary electrodes, making use of the square waves. The voltammetry method that is used for electrochemical measurements, in which a series of regular voltage pulses are superimposed on stairsteps is known as differential pulse voltammetry.

Interpretation Introduction

(d)

Interpretation:

The RDE and the ring disk electrode needs to be differentiated.

Concept introduction:

The Ring disk electrode is a type of an electrode which is in shape of a ring, that is kept in isolation from the center of the disk. A rotating disk electrode refers to a double working electrode that is used in the hydrodynamic voltammetry. This type of electrode rotates during the experiments.

Answer to Problem 25.1QAP

The difference between RDE and the ring disk electrode is that in the RDE, there is only one disk whereas in the ring disk electrode, there are more than one electrode present.

Explanation of Solution

RDE stands for a rotating disk electrode. In RDE electrode, a single disk is used. In ring disc electrode, a second ring shaped electrode is also used. This electrode is also alienated from the center of the disk. When an electroactive species is started upon the disk, the disk gets swept past the ring and undergoes another chemical reaction of the cell.

Interpretation Introduction

(e)

Interpretation:

The Faradaic impedance and double layer capacitance needs to be differentiated.

Concept introduction:

The electrolyte and the electrode together form a capacitor. The capacitance of this capacitor is called double layer capacitance. The capacitance and the resistance that acts together on the surface of the electrodes of the cell is referred to as the faradaic impedance.

Answer to Problem 25.1QAP

Double layer capacitance includes the entire orientation of the charged species at the interface of the solution of the electrode. Faradaic impedance is used to model an electron-mass transfer process that takes place in the electrochemical cell. These processes are dependent upon the frequency.

Explanation of Solution

The Double layer capacitance takes into consideration, the complete arrangement of charged species at the electrode solution interface. On the other hand, the Faradaic impedance models only the electron-mass transfer process, that takes place inside the cell. It starts acting as a capacitor when the potential across the interface is altered or changed.

Interpretation Introduction

(f)

Interpretation:

The limiting and diffusing current needs to be differentiated.

Concept introduction:

The current that is caused due to the diffusion of the charge carriers is referred to as the diffusion current whereas the limiting value of the faradaic current is known as the limiting current.

Answer to Problem 25.1QAP

Limiting current does not depend over any chemical potential which is applied, while the diffusion current always dependson the chemical potential gradient.

Explanation of Solution

Limiting current is linearly proportional to the reactants concentration and also depends upon the rate of transfer of the reactant to surface of the electrodes.

Limiting current is known as diffusion current when the transport of reactant takes place with the help of diffusion or migration except for convection.

Interpretation Introduction

(g)

Interpretation:

The laminar and turbulent flow needs to be differentiated.

Concept introduction:

In turbulent flow, there is always an irregular and uneven motion and flow of the individual fluid layers. This results in non-constant velocity of the flow of fluid.Laminar flow is a type of fluid flow in which the layers of the fluid follow a smooth, even, organized and uniform motion or path thereby never intersecting one another. In this flow, the velocity of the fluid is constant at every point within the fluid.

Answer to Problem 25.1QAP

Laminar flow is a type of flow in which the layers of the fluid glide over one another in a regular fashion and organized orientation or manner. On the other hand, the turbulent flow is a type of flow in which the layers of the fluid flow in an irregular fashion or manner.

Explanation of Solution

Turbulent flow is the flow in which the fluid layers flow in an irregular manner whereas laminar flow is a flow in which fluid layers slide over each other in a regular manner. In laminar flow, the movement of the layers remains parallel to surface of the electrode. In the turbulent flow, the movement of the fluid layers is in form of a zigzag or crisscross pattern.

Interpretation Introduction

(h)

Interpretation:

The standard electrode potential and half wave potential needs to be differentiatedfor a reversible reaction at a working electrode.

Concept introduction:

Half wave potential refers to the potential at which the polagraphic wave current becomes equal to one half of diffusion current. Standard electrode potential is a way or method of individual potential of the reversible electrode at a standard state with the ions at an effective concentration.

Answer to Problem 25.1QAP

The standard electrode potential indicates the strength of the individual potentials of the reversible electrodes at a specified standard state. At half wave potential, the polagraphic wave current is generally half of the diffusion current and remains the same for each of the elements and their different valence states and forms.

Explanation of Solution

Half wave current is different for each element, even for the different valence states and forms of the same element whereas the standard electrode potential is the magnitude of the individual potentials of the reversible electrodes at a standard state. The potential at which the polagraphic wave current is equal to the half of the diffusion current, is known as the half wave potential.

Interpretation Introduction

(i)

Interpretation:

The normal adsorptive stripping methods needs to be differentiated.

Concept introduction:

In adsorptive stripping, the preconcentration is never controlled or varied by electrolysis. It is achieved by adsorption on the working electrode. Normal stripping method refers to the anodic stripping voltammetry method. In this method, the desired analyte is first electroplated on the electrode and then oxidized from the electrode during the stripping step or process.

Answer to Problem 25.1QAP

In normal stripping, the analyte is deposited either on a drop or in a film of mercury whereas in adsorptive stripping, the analyte is deposited directly by means of physical adsorption.

Explanation of Solution

In adsorptive stripping, the analyte gets placed due to the process of physical adsorption unlike normal stripping.In both of the stripping methods, estimating the deposition of the analyte by means of stripping needs the same procedure and steps.