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CHEM 23 > potentiometry > Flashcards

potentiometry Flashcards

1
Q

based on the measurement of the potential of electrochemical cells without drawing appreciable current

A

potentiometry

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2
Q

no current or only a negligible current flows while measuring a solution’s potential, the solution’s composition remains unchanged

A

quantitative technique

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3
Q

made using a potentiometer to determine the difference in potential between a working or, indicator, electrode and a counter electrode

A

potentiometric measurements

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4
Q

a half cell with an accurately known electrode potential Eref that is independent of the concentration of the analyte or any ions in the solution

A

reference electrode

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5
Q

has a potential Eind that varies in a known way with variation in the concentration of an analyte

A

indicator electrode

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6
Q

has a potential that is accurately known, constant, and completely insensitive to the composition of the analyte solution

A

ideal reference electrode

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7
Q

seldom used as a reference electrode for day to day potentiometric measurements because it is somewhat inconvenient to use and maintain and is also a fire hazard

A

standard hydrogen electrode (SHE)

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8
Q

what is an ideal indicator electrode

A

responds rapidly to changes in the concentration of an analyte ion and is selective to a group of ions

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9
Q

types of indicator electrode

A
  1. metallic
  2. membrane electrodes
  3. ion-sensitive field effect transistor (ISFET)
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10
Q

types of metallic indicator electrode

A
  1. electrode of the first kind
  2. electrodes of the second kind
  3. Inert electrode
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11
Q

potential difference is created

A

membrane electrodes

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12
Q

characteristics of membrane

A
  1. low solubility
  2. some electrical conductivity
  3. selectivity
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13
Q

two general types of membrane electrodes

A

crystalline and non crystalline membranes

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14
Q

non crystalline membranes

A
  1. glass - silicate glasses for H+ , Na+
  2. liquid - liquid ion exchanger for Ca2+
  3. immobilized liquid - liquid/PVC matrix for Ca2+ and NO3-
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15
Q

glass membrane structure

A
  1. SiO4⁴- framework with charge balancing cations
  2. SiO2 72%, Na2O 22%, CaO 6%
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16
Q

by altering the glass composition

A

direct potentiometric measurement of single charge cation could be done

17
Q

glass electrodes for these analytes are available

A

Na+, K+, NH4+, Rb+, Cs+, Li+

18
Q

based on potential that develops across two immiscible liquids with different affinities for analyte

A

liquid membrane electrodes

19
Q

porous membrane used to separate liquids

A

liquid membrane electrodes

20
Q

the potential develops across the interface between the solution containing the analyte and the ion exchanger

A

liquid membrane electrodes

21
Q

the reservoir forces exchanger into the membrane; the exchanger forms complexes with the species of interest

A

calcium electrode

22
Q

crystalline membranes

A
  1. single crystal - LaF3 for F
  2. mixed crystal - AgS for S2- and Ag+
23
Q

usually ionic compound

A

crystalline membrane electrodes

24
Q

single crystal, crushed powder, melted and formed

A

crystalline membrane electrodes

25
Q

sometimes doped (Li+) to increase conductivity

A

crystalline membrane electrodes

26
Q

operation similar to glass membrane

A

crystalline membrane electrodes

27
Q

other potentiometric sensors

A
  1. gas sensors
  2. biosensors
28
Q

gas membrane allows small gas molecules to pass and dissolve into internal solution

A

gas sensors

29
Q

an analytical device for the detection of an analyte that combines a biological component with a physicochemical detector component

A

biosensor

30
Q

make use of biocomponents capable of recognizing (bio) chemical species and transforming them into a product through a chemical reaction

A

catalytic

31
Q

working range for most ion-selective electrodes is from a maximum concentration of _______ to a minimum concentration of _________

A

maximum: 0.1 - 1 M
minimum: 10-⁵ - 10-10 M

32
Q

errors in potentiometry may be due to

A
  1. interfering ions
  2. finite current drawn through the cell while measuring the potential
  3. difference in the analyte’s activity coefficient in the sample and standard solutions
  4. liquid junction potentials
33
Q

precision of potentiometric measurement is limited to

A

variation in temperature and the sensitivity of the potentiometer

34
Q

selectivity of potentiometry

A

most ion-selective electrodes respond to more than one analyte

35
Q

potentiometry provides what in terms of completing methods

A

rapid and relatively low cost means for analyzing samples

CHEM 23 (7 decks)

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