List types of indicator electrod and their differences
1-Type one: measures its own ion
Ex: Cu is measured with CuSO4 electrode
2- Type two: Measures conc. of anions in which the metal cation forms precipitate
Ex: cl is measured with Ag electrode
3- Type three: Measures different cations with the same charge as the elctrode
Ex: Ca is measured with Hg electrode
4- Redox electrode: uses inert metal (Pb,Pd) and act as an indicator electrode( surface for electron exchange)
When is Redox electrode used and what is the difference between redox and indicator electrode?
When Non of the three indicator electrods work becasue the analyte which is being measured is not a metal, or for some metals a good electrode can not be made.
Indicator electrods can give quantitative analysis but No quantity ( Number) will be given in Redox electrod.
How does Redox electrod measures the analyte
It gives ratio of the ions
Two main classes of membrane electrodes
Ion Selective (ISE)
Molecular selective
Membrane selectively reacts with analyte ion by _________,__________, and__________
ion exchange
crystallization
complexation
properties of ISE membrane
minimal solubility in analyte
exhibits electrical conductivity
reacts wtih analyte by ion exchange, crystallization, and complexation
Crystalline membrane and glass membrane are two types of _____
ISE membrane
What is the difference between crystal and glass
Crystal has a uniform pattern in their structure
glass structure is random
E* is determined through ______________
external standards
pH electrode is a type of _________________ membrane
non-crystalline glass
pH response is due to ___________
external [H3O+] (out side of membrane)
How does the surface of ISE knows what type of ions are present?
it is called ISE which means it selects types of ions which it will interact with through SiO2 membrane
The pH electrode consists of _______________ electrode, Ex:_________, and _________ electrode, Ex:___________. It works as a result of _________
External reference electrode Ex: Calomel, Ag/Agcl
Internal reference electrode Ex: Ag/AgCl
ion exchange between the analyte and hydrated surface of glass membrane
H+ taken up by the glass membrane depends on the solution conc.(T/F)
True
what does the constant of the pH electrode depend on?
standard buffers
It depends on:
External and internal refernce
Junction potential
Asymmetry potential ( When solutions in both side of the membrane have the same conc. the reading is not zero)
non-crystalline liquid membrane formed from___________
lmmiscible liquids that form bonds with selective ions
Fluoride ISE uses _____ crystal of ________ and conductivity that happens due to F- movement through the lattice is enhanced by ____ with ________and _________ ions.
single, LaF3
Dopping, Eu2+ and Ca2+
________ ion fixes the potential of the _______- Ag/AgCl ref. el.
________ ion controls the potential of the ___ surface of the LaF3 crystalline membrane
Cl-, internal
F-, inner
In Flouride ISE, how would you solve OH- interferences above pH of 8
Lower the pH , if possible
Use buffer solution, TISAB
Flouride activity depends on:
Ionic strength
pH
Presence of complexing species ( Al interfer with F- even at low conc.)
Two types of molecular selective electrode
Gas sensing
enzyme
Gas sensing electrode is type of _______________ electrode which consists of __________electrode and __________ electrode. It is used to analyze________ or ions that can be converted to _______ gases by adjusting the ________.
Molecular selective electrode
pH, reference
dissolved gases
dissolved
pH
In molecular selective electrode sample are in close contact with elctrodes. (T/F)
False. No electrode is in direct contact with sample because of the plastic membrane
