Ch 21 Potentiometry

Question 1

is a half-cell
having a known electrode potential
that remains constant at constant
temperature and is independent of the
composition of the analyte solution.

Answer 1

A reference electrode

Question 2

Dictate the representation of cell

Answer 2

reference electrode|salt bridge|analyte solution|indicator electrode

Question 3

An _______ has a potential
that varies in a known way with variations in the concentration of an analyte. It is immersed in a solution of the analyte

Answer 3

indicator electrode

Question 4

__________ is a nearly ideal electrolyte for the salt
bridge because ________

Answer 4

Potassium chloride; the mobilities of the K1 ion and the Cl2 ion are nearly equal.

Question 5

Formula for the potential of the cell

Answer 5

Ecell = Eind - Eref + Ej

Question 6

Strictly, the potential of a galvanic cell is related to the

Answer 6

activity of the analyte.

Question 7

An electrode that has a potential that is accurately known, constant, and completely insensitive to the composition of the analyte solution. In addition, this electrode should be rugged, easy to assemble, and should maintain a constant potential while passing minimal currents.

Answer 7

reference electrode

Question 8

consist of mercury in contact with a solution that is saturated with mercury(I) chloride (calomel) and that also contains a known concentration of potassium chloride

Answer 8

Calomel reference electrodes

Question 9

All calomel electrodes are saturated
with

Answer 9

Hg2Cl2 (calomel).

Question 10

, which is available as translucent
flakes, is a heteropolysaccharide that
is extracted from certain East Indian
seaweed.

Answer 10

Agar

Question 11

The most widely marketed reference electrode system consists of a silver electrode
immersed in a solution of potassium chloride that has been saturated with silver
chloride

Answer 11

Silver Chloride Reference Electrodes

Question 12

Advantage of Silver Chloride Reference Electrodes from Calomel Reference Electrodes

Answer 12

Silver–silver chloride electrodes can be used at temperatures greater than 60°C, while calomel electrodes cannot.

Question 13

When two electrolyte solutions of different composition are in contact with one another, the ____________ potential difference across the interface is created due to the unequal distribution of cations and anions across the boundary

Answer 13

Liquid-Junction Potentials

Question 14

The magnitude of the Liquid-Junction Potentials can be minimize by placing a ______ between the two solutions

Answer 14

salt bride

Question 15

three types of Indicator electrodes

Answer 15

metallic Indicator electrodes
membrane Indicator electrodes
ion-sensitive field effect transistors.

Question 16

Classification of metallic indicator electrodes

Answer 16

electrodes of the first kind
electrodes of the second kind
inert redox electrodes

Question 17

is a pure metal electrode that is in direct equilibrium
with its cation in the solution. A single reaction is involved.

Answer 17

electrode of the first kind

Question 18

a metal electrode that does not only serves as indicator electrodes for its own cations, but also respond
to the activities of anions that form sparingly soluble precipitates or stable complexes with such cations.

Answer 18

Electrodes of the Second Kind

Question 19

relatively inert conductors such as platinum, gold, palladium, and carbon, can be used to monitor
redox systems.

Answer 19

inert metallic redox electrodes

Question 20

membrane electrode that separates two solutions with different hydrogen ion concentrations is called

Answer 20

p-ion electrodes

Question 21

What part of the glass/ calomel cell responds to the pH

Answer 21

the thin glass membrane bulb at the tip of the electrode

Question 22

Glasses that has a pH function and absorb water are said to be

Answer 22

hygroscopic

Question 23

Glasses that show no pH function and does not absorb water are said to be

Answer 23

Nonhygroscopic

Question 24

Why do we need to hydrate the glass membrane of an electrode before it will function as a pH electrode?

Answer 24

Because hygroscopic glasses are pH-sensitive.
The hydration of a pH-sensitive glass membrane involves an ion-exchange reaction between singly charged cations in the interstices of the glass lattice and hydrogen ions
from the solution.

Question 25

What are the four membrane potentials that develop in a cell when pH is being determined with a glass electrode?

Answer 25

The 2 reference electrode potentials from the solution The junction potential, Ej, across the salt bridge Lastly, the boundary potential, Eb, which varies with the pH of the analyte solution.

Question 26

Three components of the potential of a glass indicator electrode, Eind

Answer 26

(1) the boundary potential Eb (2) the potential of the internal Ag/ AgCl reference electrode (3) the small asymmetry potential, Easy

Question 27

Formula for the glass indicator electrode, Eind

Answer 27

Eind = Eb + EAg/AgCl + Easy

Question 28

is a measure of the response of an ionselective electrode to other ions.

Answer 28

The selectivity coefficient

Question 29

Errors that glass electrode exhibit

Answer 29

Alkaline error Acid error

Question 30

is a saturation effect that occurs when all the surface sites on the glass are occupied with H+ ions. Under these conditions, the electrode no longer responds to further increases in the H1 concentration, and the pH readings are too high.

Answer 30

acid error

Question 31

The ________ disk is porous toward organic liquids but repels water.

Answer 31

hydrophobic

Question 32

ISFETs stands for

Answer 32

ion-sensitive field effect transistors.

Question 33

is a tiny solid-state semiconductor device that is widely used in computers and other electronic circuits as a switch to control current flow in circuits

Answer 33

field effect transistor or metal oxide field effect transistor (MOSFET),

Question 34

offer a number of significant advantages over membrane electrodes including ruggedness, small size, inertness toward harsh environments, rapid response, and low electrical impedance.

Answer 34

ISFETs

Question 35

is a galvanic cell whose potential is related to the concentration of a gas in a solution.

Answer 35

gas-sensing probe

Question 36

is fabricated from a hydrophobic polymer. The membrane is highly porous (the average pore size is less than 1 mm) and allows the free passage of gases

Answer 36

microporous membrane

Question 37

pH meters are frequently used for the measurement of concentrations of other ions, it is also called

Answer 37

p-Ion meters or ion meters

Question 38

The technique requires only a comparison of the potential developed in a cell containing the indicator electrode in the analyte solution with its potential when immersed in one or more standard solutions of known analyte concentration

Answer 38

Direct potentiometry

Question 39

For direct potentiometric measurements, the potential of a cell can then be expressed in terms of the potentials developed by the indicator electrode, the reference electrode, and a junction potential,

Answer 39

Ecell = Eind - Eref + Ej

Question 40

Electrode response is related to analyte _____ rather than analyte concentration

Answer 40

Activity

Question 41

is used to control the ionic strength and the pH of samples and standards, in ion-selective electrode measurements.

Answer 41

total ionic strength adjustment buffer (TISAB)

Question 42

involves determining the potential of the electrode system before and after a measured volume of a standard has been added to a known volume of the analyte solution. Multiple additions can also be made.

Answer 42

The standard addition method

Question 43

Errors Affecting pH Measurements

Answer 43

Alkaline error The acid error Dehydration Errors in low ionic strength solutions Variation in junction potential Error in the pH of the standard buffer

Question 44

This happen when the ordinary glass electrode becomes somewhat sensitive to alkali metal ions and gives low readings at pH values greater than 9

Answer 44

Alkaline error.

Question 45

This happen when the Values registered by the glass electrode tend to be somewhat high when the pH is less than about 0.5.

Answer 45

The acid error

Question 46

This causes erratic electrode performance.

Answer 46

Dehydration

Question 47

It has been found that significant errors (as much as 1 or 2 pH units) may occur when the pH of samples of low ionic strength, such as lake or stream water, is measured with a glass/calomel electrode system

Answer 47

Errors in low ionic strength solutions

Question 48

A fundamental source of uncertainty for which a correction cannot be applied, resulting from differences in the composition of the standard and the unknown solution.

Answer 48

Variation in junction potential

Question 49

Any inaccuracies in the preparation of the buffer used for calibration or any changes in its composition during storage cause an error in subsequent pH measurements.

Answer 49

Error in the pH of the standard buffer

Question 50

we measure the potential of a suitable indicator electrode as a function of titrant volume

Answer 50

potentiometric titration,

Question 51

The four membrane potentials that develop in a cell

Answer 51

Reference electrode potential Junction potential Boundary potential