LECTURE - Potentiometry

Question 1

what is POTENTIOMETRY?

Answer 1

• An analytical method where you measure the electrical potential (voltage) of an electrochemical cell without letting any significant current flow.
• We measure the voltage → then relate it to the concentration of the analyte.

Question 2

4 components of a Potentiometric Cell

Answer 2

1. Reference electrode
2. Salt bridge
3. Analyte
4. Indicator electrode

Question 3

Basis Equation for Potentiometry

Answer 3

E cell = E ind - Eref + Ej

Question 4

5 properties of Reference Electrode

Answer 4

• Half-cell with known potential (Eref)
• Left hand electrode (by convention)
• Easily assembled
• Stable over time concentration

Question 5

is reference electrode reversible?

Answer 5

YES + obeys Nernst equation

Question 6

3 properties of Indicator Electrode

Answer 6

• Generates a potential (Eind) that depends on analyte concentration
• Selective
• Rapid and reproducible response

Question 7

____ generates Ej (liquid junction) which is ____

Answer 7

salt bridge

negligible (bc its effect is minimal)

Question 8

what is liquid junction?

Answer 8

Ej

• boundary/interface between 2 solutions (contain diff electrolytes or diff concentration of electrolytes)

Question 9

liquid junction is caused by?

Answer 9

unequal mobilities (or diffusion speed) of + and - ions

Question 10

2 types of INDICATOR ELECTRODES

Answer 10

1. Metallic IE (direct)
   A. Electrodes of the First Kind
   B. Electrodes of the Second Kind
   C. Inert Metallic Electrodes
2. Membrane IE (ion selective)
   A. Glass membrane: for cations (pH IE)
   B. Liquid Membrane IE (ion exchange principle)

Question 11

difference between the 3 types of METALLIC IE

Answer 11

A. Electrodes of the First Kind
- pure metal electrode in contact with its cation

B. Electrodes of the Second Kind
- metal coated with salt (forms ppt/stable complex)

C. Inert Metallic Electrodes
- inert conductors that facilitate electron movement (redox rxns)
- thus, are electron source/sink

Question 12

4 disadvantages of Electrodes of First Kind

Answer 12

• Not very selective
• pH dependent (dissolves at specific pH)
• easily oxidized
• non-reproducible

Question 13

disadvantage of inert metallic electrode?

Answer 13

may not be reversible

Question 14

3 examples of inert metallic electrode?

Answer 14

Pt, Au, Pd

Question 15

Determine the type of solutions that each of the ff can measure:

A. Inert electrode
B. Metallic of First Kind
C. Metallic of Second Kind
D. Membrane Electrode

Answer 15

A. Redox
B. Redox
C. Ksp
D. Ions and Gases

Question 16

Is Membrane IE selective and specific?

Answer 16

selective but not specific (prefers specific ions but interference still occurs)

Question 17

what IE is most widely used in different industries and research?

+ specific environments they are suitable in?

Answer 17

Membrane IE

• in situ
• online
• field applications

Question 18

type of membrane IE that can be used in situ + applications (2)?

Answer 18

Ion Selective Electrode

• for real time monitoring (point of care devices & environmental application)