Potentiometry Extra practice
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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
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 _____
What is the difference between crystal and glass
- Crystal has a uniform pattern in their structure
- glass structure is random
E* is determined through ______________
pH electrode is a type of _________________ membrane
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)
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
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
- Presence of complexing species ( Al interfer with F- even at low conc.)
Two types of molecular selective electrode
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
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
What is the interferences in DO electrode
Molecules with same size and shape as O2
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