Potentiometry And Electrodes

Question 1

What is Q in potentiometry

Answer 1

Electric charge

Question 2

What are the electrodes in potentiometry

Answer 2

A reference electrode
A indicator (working) electrode

Question 3

What is the reference electrode

Answer 3

A half cell with a constant potential (as long as temp stays constant, and concentration)

Question 4

What is the indicator(working) electrode

Answer 4

The electrode that responds to analyte activity, has a pt wire that measures charge

Question 5

What does the salt bridge have and what does it do

Answer 5

Has gel that has electrolyte (kno3)

Separates reactants into two half cells so redox happens in two separate containers, ground the solutions so that measured potential is right

The k+ moves into Cathode

The no3- moves into anode

This replenishes the lost charges that flow though the light bulb

Question 6

How is the potential staying constant in reference electrode

Answer 6

The dissolving and precipitating equilibrium (Ksp) in a saturated solution keeps the concentration of dissolved ions constant

Question 7

What makes up the single junction reference electrode

Answer 7

Djjdsjnd

Question 8

What is a saturated calomel electrode

Answer 8

SCE

A liquid mercury electrode saturated with kcl

Question 9

Subtract potentials

Answer 9

Idk

Question 10

What are the two classes of indicator electrodes

Answer 10

Metal electrode: create a electric potential response to a redox reaction at the surface of the metal

Ion selective electrode: binding one specific type of ion to a membrane makes a electric potential (instead of redox signal it make junction potential)

Question 11

What is a junction potential

How does it develop

Why is it a problem

Answer 11

The voltage difference that’s in between two different electrolyte solutions

Is made because of opposite charged ions having different mobilities (ionic strengths)

Limits the accuracy of measurements because we don’t know the size of the junction potential

Question 12

Give junction potential example

Answer 12

In nacl the cl ions diffuse into water faster than the na.

This makes a charge separation where the nacl salt bridge touches water

Question 13

How do we minimize Ejinction

Answer 13

Kcl salt bridge
Ionic liquid based salt bridge

Question 14

What are porous glass plugs for in a slat bridge

Answer 14

To keep the salt in the beige while still letting ions current in the half cell to flow through

Question 15

What are nanoporous glass plugs

Answer 15

4-20nm pore size

Smaller pores which help more specific ions to pass

Less stable junction potentials

Question 16

What are microporous glass plugs

Answer 16

100-3000nm

Best for measurement

Larger pores so less selectivity

More stable junction potentials

Question 17

Ion selective diagram

Answer 17

Ok

Question 18

What 3 things does the ion selective glass electrode consist of

Answer 18

Outer ag|agcl electrode (has solid kcl and solid agcl)

Selective h+ glass membrane

Inner ag|agcl electrode (has buffered kcl with agcl)

Question 19

What is the glass membrane of the glass ph combo electrode made of

Answer 19

SiOH (silica)
Pores that are coated with negative charged O- atoms
Na+ ion that move through the pores (slowly)

It’s slightly conductive

Question 20

How are hydrated gel layers formed

Answer 20

Two surfaces of the ph sensing glass membrane absorb water which froms it (basicallymelted glass)

Question 21

What is the cell notation of the ph sensing glass electrode

Answer 21

Check pics

Question 22

What are the 10 errors in glass ph measurements

Answer 22

1. Standard buffer uncertainty (standards are only accurate to +/- 0.01
2. Junction potential uncertainty
3. Junction potential drift error
4. Concentrated Sodium error
5. Strong acid error
6. Equilibrium time error
7. Hydration of glass initialization error
8. Temperature error
9. Dirty electrode
10. Stirring error

Question 23

How do you minimize junction potential uncertainty

Answer 23

By calibration the same ionic strength as the analyte solution

Question 24

How do you minimize junction potential drift error

Answer 24

By calibrating every two hours

Question 25

How do you minimize concentrated sodium error

Answer 25

Avoid using NAOH because glass electrodes respond to na+

Question 26

How do you minimize dirty electrodes

Answer 26

Avoid hydrophobic substances

Question 27

What are the advantages of ion selective electrodes

Answer 27

Less expensive
Respond linearly in log form
Wide range
Non destructive
Short reposnse time
Unaffected by colour or clarity of liquid (turbidity)

Question 28

What are the disadvantages of ion selective electrodes

Answer 28

Fragile
Small shelf life
Need constant ionic strength
Uncomplexed ions only
Interference
Can be fouled by protiens

Question 29

Does the ISE respond to a specific ion or it is selective

Answer 29

Selective

Question 30

What are the types of ion selective electrodes and what are each for

Answer 30

Glass membranes (h and Monovalent cations)
Solid state electrodes (inorganic crystals or conductive polymers)
Liquid based electrodes (hydrophobic polymer membrane with a hydrophobic liquid ion exchanger)
Compound electrodes (electrodes enclosed by a membrane the separates analyte from other species or genterate and analyte)