Electroanalytical Tech Chapter 2: Potentiometry

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Questions and Answers

Which of the following is a characteristic of a reference electrode?

Sensitive to analyte concentration

Is an indicator electrode

Has a constant potential (correct)

Is difficult to assemble

What is the main purpose of a salt bridge in a potentiometric cell?

To connect the reference electrode to the indicator electrode (correct)

To increase the current flowing through the cell

To separate the analyte from the electrodes

To measure the potential of the cell

What type of electrode is sensitive to the analyte concentration?

Analyte electrode

Reference electrode

Indicator electrode (correct)

Salt bridge

What is the Nernst equation used for in potentiometry?

To determine the concentration of an analyte Signup and view all the answers

What is the primary application of potentiometry?

Pharmaceutical assay and industrial analysis Signup and view all the answers

What is the purpose of the indicator electrode in a potentiometric cell?

To measure the potential of the cell Signup and view all the answers

Which of the following is an example of a reference electrode?

All of the above Signup and view all the answers

What is the function of a potentiometric cell?

To measure the concentration of an analyte Signup and view all the answers

What is the primary function of a metal indicator electrode of the second kind?

To determine the concentration of an interacting ion Signup and view all the answers

What type of electrodes are chemically inert and do not actively take part in the redox process?

Inert electrodes Signup and view all the answers

What determines the voltage created at an inert electrode?

The type and concentration of redox reagents in the solution Signup and view all the answers

What is the equation that relates the cell potential Ecell to the indicator electrode potential Eind and the reference electrode potential Eref?

Ecell = Eind - Eref + Ej Signup and view all the answers

What is the purpose of a metal indicator electrode of the second kind in direct analysis?

To determine the concentration of an interacting ion Signup and view all the answers

What is the characteristic of a membrane electrode's potential?

It is created by an uneven charge accumulation at the opposite surface of a unique membrane Signup and view all the answers

What is the equation that relates the indicator electrode potential Eind to the standard electrode potential Eo and the concentration of the ion Cu2+?

Eind = Eo - 0.05916/n log1/[Cu2+] Signup and view all the answers

What is the purpose of reference electrodes in potentiometric cells?

To provide a stable potential for the measurement of the indicator electrode potential Signup and view all the answers

What is the composition of glass membranes in a pH electrode?

72% SiO2, 28% CaO, BaO, Li2O, Na2O, and/or Al2O3 Signup and view all the answers

What is the ion exchange process that occurs at the glass membrane-solution interface?

Gl– + H+ = H+Gl– Signup and view all the answers

What is the relationship between Ecell and log[H+] in a pH electrode?

Ecell is directly proportional to log[H+] Signup and view all the answers

What type of electrode is used for the determination of F-?

LaF3 membrane electrode Signup and view all the answers

What is the equation used in the standard addition method for quantitative analysis?

2{-ECell / 0.05916} = log {Vsam /VTot + Vstd Cstd / VTot Csam} Signup and view all the answers

What type of electrode is used for the determination of X-?

AgX membrane electrode Signup and view all the answers

What is the purpose of the reference electrode in a potentiometric cell?

To provide a stable reference point for the cell Signup and view all the answers

What type of electrode is classified as an electrode of the first kind?

Ag/AgCl electrode Signup and view all the answers

Study Notes

Potentiometric Measurements

Potentiometric method measures the potential of an electrochemical cell with little to no current flowing through the cell.
It involves measuring the potential between two electrodes submerged in the fluid to be examined.
Two electrodes are required: an indication electrode and a reference electrode, along with a potentiometer.

Potentiometric Measurement in Electrochemical Cell

It is a method of analysis that determines the concentration of an ion or substance by measuring the potential developed when a sensitive electrode is immersed in the solution of the species to be determined.
Potentiometry is commonly used in pharmaceutical assay and various industrial analyses.

Components of a Potentiometric Cell

Reference electrode
Salt bridge
Analyte
Indicator electrode

Reference Electrode

A half-cell with a known potential (Eref)
Left-hand electrode (by convention)
Easily assembled, rugged, and insensitive to analyte concentration
Reversible and obeys the Nernst equation
Constant potential and returns to original potential

Types of Reference Electrodes

Standard Hydrogen Electrode (SHE)
Calomel Reference Electrode (SCE)
Silver/Silver Chloride Reference Electrode

Expression of Reference Electrode

Reference electrode must have a constant potential and its potential must be known.
Any electrode must be expressed in terms of the redox reaction occurring at the electrode surface.
Nernst equation and half-cell are used to express the electrode.

Metal Indicator Electrode

Can be used to measure an interacting ion
Prior to analysis, it is necessary to know the metal ion's initial concentration
Can be used for direct analysis of analyte solutions as well as titrations

Inert Electrodes

Chemically inert and conductors, such as carbon, platinum, or gold
Do not actively take part in the redox process
The voltage created at an inert electrode depends on the type and concentration of different redox reagents in the solution

Membrane Indicator Electrodes

The membrane electrode's potential is created by an uneven charge accumulation at the opposite surface of a unique membrane
The location of an equilibrium involving analyte ions, which depends on the concentration of those ions in the solution, determines the charge at each surface

Glass Membrane Electrode (pH Electrodes)

Composition of glass membranes: 72% SiO2, 28% CaO, BaO, Li2O, Na2O, and/or Al2O3
Ion exchange process at glass membrane-solution interface
Ecell is directly proportional to log [H+]

Glass Electrodes of Other Cations

Glass electrodes can be used to determine other cations, such as Na+, K+, and Ca2+

Liquid Membrane Electrodes

Used for the determination of certain ions, such as Ca2+, Ba2+, and Cl-

Crystalline-Membrane Electrodes

Used for the determination of specific ions, such as F-, Cl-, and S2-
Examples: AgX membrane, Ag2S membrane, and LaF3 membrane

Quantitative Analysis – Standard Addition Method

Used for the quantitative analysis of ions
Formula: 2-ECell / 0.05916 = log {Vsam / VTot + Vstd Cstd / VTot Csam}
Example: calculation of the concentration of S-2 ions using the standard addition method

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Description

This quiz covers the basics of potentiometric measurements, a technique used in electroanalytical technology to measure the potential of an electrochemical cell with little to no current flow.