What is the definition of potentiometry?
![card image](../uploads/527/53/_15fed498_1867048583f__8000_00003550.png)
measurement of the electrical potential difference between two
electrodes in an
electrochemical cell, when no current is
allowed to flow.
What is the definition of oscillating reactions?
![card image](../uploads/387/12/_15fed498_1867048583f__8000_00003261.gif)
in which chemical concentrations oscillate between high and low values.
What is the definition of junction potential?
![card image](../uploads/388/13/_15fed498_1867048583f__8000_00003263.png)
When two dissimilar electrolyte solutions are placed in contact, a voltage difference develops at the interface.
What is the difference between direct and relative potentiometric measurements?
Direct
- Inherent inaccuracy
Liquid-liquid junction at 4% among 14 measurements by direct potentiometry
- different indicator electrodes
- varying liquid junction potential
Relative
- By titration
- relatively precise
- permit an end point to be identified with little uncertainty
What is a junction potential?
- Caused by unequal mobility of different ions at liquid-liquid interfaces.
- Unknown junction potentials can result in a limitation of accuracy of potentiometric measurements.
What are double-junction reference electrodes used for?
typically used for ISE [Ion selective electrode] analysis where the leached electrolyte must not interfere with the ISE being used.
They are also particularly useful for pH analysis of products that must not have KCl or a strong electrolyte contaminating the sample
What is an ISE and what are some advantages?
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is an analytical technique used to determine the activity of ions in aqueous solution by measuring the electrical potential.
- It is relatively inexpensive and easy to operate.
- It has wide concentration measurement range.
- As it measure the activity, instead of concentration, it is particularly useful in biological/medical application.
- It is a real-time measurement, which means it can monitor the change of activity of ion with time.
- It can determine both positively and negatively charged ions.
What is the function of an ISE (Ion-selective electrode)?
selectively binds one ion—no redox chemistry
What is the function of a Metal electrode?
It is a surface on which redox reaction takes place.
How does a glass pH electrode work?
- pH glass surfaces from a hydrate gel in water where metal diffuses out and H+ in.
- an ion exchange equilibrium occurs
- the porous plug serves as the salt bridge.
What are different errors of pH measurement?
- Standards{Buffer accuracy}
- Junction potential {analyte composition different that electrode}
- Junction potential drift{ precipitate in the plug recalibrate pH meter }
- Sodium error{ H+ is low Na+ is high}
- Acid error{glass is saturated with H+}
- Equilibrium time{ didn't wait for pH to equilibrate}
- Hydration of Glass{ electrode too dry}
- Temperature{pH meter not at same temp as sample}
- Cleaning{probe has hydrophobic liquid}
What is a combination electrode?
![card image](../uploads/399/24/_15fed498_1867048583f__8000_00003275.gif)
incorporating both the glass and reference electrodes in one body
What should be done to pH electrode before use?
They must be calibrated before use. It should be calibrated every 2 h in sustained use. Ideally, calibration standards should bracket the pH of the unknown.
What should you not do to a glass electrode?
Don’t leave it out of water (or in a nonaqueous solvent) longer than necessary.
What are some advantages and disadvantages of ISE (Ion-selective electrode)?
Advantages:
- unaffected by color turbidity
- short response time
- Non-contaminating
Disadvantages:
- electrodes can be fouled by organic solutes
- precision ≤ 1%
- certain ions can interfere
What is a solid-state ion-selective electrode?
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- Inorganic crystal act as the membrane
- ion of interest moves through the crystal lattice by going to each vacant site.
What is a liquid-based ion-selective electrode?
![card image](../uploads/401/26/_15fed498_1867048583f__8000_00003279.png)
- uses a hydrophobic membrane that contains a liquid organic complexing agent that reacts selectively with the analyte
- Potential difference builds up between inside and outside of the membrane depending on the analyte.
What is a compound electrode?
a conventional electrode surrounded by a membrane that isolates (or generates) the analyte to which the electrode responds.
- Electrode have membrane of multiple type
What are the different types of membrane electrodes?
There are four main types of ion-selective membrane used in ion-selective electrodes (ISEs): glass, solid state, liquid based, and compound electrode.
What is the quantity, method, and analyte for potentiometry?
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- Quantity: potential voltage
- Unit: voltage
- Analyte: H+ and PCO2
What is the quantity, method, and analyte for coulometry?
![card image](../uploads/528/54/_15fed498_1867048583f__8000_00003554.png)
- Quantity: Electric charge
- Unit: Coulombs
- Analyte: Cl-
What is the quantity, method, and analyte for amperometry?
![card image](../uploads/529/55/_15fed498_1867048583f__8000_00003566.png)
- Quantity: Current
- Unit: Ampere
- Analyte:PO2
What is the quantity, method, and analyte for voltammetry?
![card image](../uploads/530/56/_15fed498_1867048583f__8000_00003562.png)
- Quantity: Current
- Unit: Volt
- Analyte: Vitamin C