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Questions and Answers
What is the standard reduction potential ($E^o$) for the silver-silver chloride (Ag/AgCl) electrode?
What is the standard reduction potential ($E^o$) for the silver-silver chloride (Ag/AgCl) electrode?
- +0.268 V
- +0.197 V
- +0.222 V (correct)
- +0.241 V
The electrode potential of a Ag/AgCl reference electrode depends primarily on which factor?
The electrode potential of a Ag/AgCl reference electrode depends primarily on which factor?
- The concentration of $K^+$ ions.
- The concentration of $Ag^+$ ions.
- The concentration of $AgCl$ solid.
- The concentration of $Cl^-$ ions. (correct)
What is the main purpose of using a high concentration of KCl in the internal solution of a Ag/AgCl reference electrode?
What is the main purpose of using a high concentration of KCl in the internal solution of a Ag/AgCl reference electrode?
- To increase the solubility of AgCl.
- To minimize variations in the $Cl^-$ concentration over time. (correct)
- To enhance the conductivity of the electrode.
- To prevent the formation of AgCl precipitates.
What type of substances are considered interferents for the Ag/AgCl reference electrode?
What type of substances are considered interferents for the Ag/AgCl reference electrode?
What is the electrode potential (E) of a Ag/AgCl electrode in saturated KCl?
What is the electrode potential (E) of a Ag/AgCl electrode in saturated KCl?
What is the primary function of the slow outward flow of the electrolyte in a reference electrode?
What is the primary function of the slow outward flow of the electrolyte in a reference electrode?
Why are double junction reference electrodes used?
Why are double junction reference electrodes used?
Which of the following is a critical characteristic of an effective indicator electrode?
Which of the following is a critical characteristic of an effective indicator electrode?
What is the electrode potential (E) of a Calomel electrode in saturated KCl?
What is the electrode potential (E) of a Calomel electrode in saturated KCl?
Why do metal indicator electrodes have limited analytical applications, especially with complex samples?
Why do metal indicator electrodes have limited analytical applications, especially with complex samples?
Which of the following is true about the standard hydrogen electrode (SHE)?
Which of the following is true about the standard hydrogen electrode (SHE)?
What distinguishes ion-selective electrodes (ISEs) from metal indicator electrodes?
What distinguishes ion-selective electrodes (ISEs) from metal indicator electrodes?
Which of the following describes the response mechanism of metal indicator electrodes?
Which of the following describes the response mechanism of metal indicator electrodes?
An ion-selective electrode's response is dependent on the analyte concentration. Where does the comparison of analyte concentration take place?
An ion-selective electrode's response is dependent on the analyte concentration. Where does the comparison of analyte concentration take place?
What is the purpose of the porous setto in the reference electrode diagram?
What is the purpose of the porous setto in the reference electrode diagram?
What is the purpose of the intermediate chamber in the reference electrode?
What is the purpose of the intermediate chamber in the reference electrode?
Which of the following practices helps maintain the accuracy of pH measurements?
Which of the following practices helps maintain the accuracy of pH measurements?
What is the primary function of the thermal probe in a pH meter?
What is the primary function of the thermal probe in a pH meter?
What does ATC stand for in the context of pH measurement?
What does ATC stand for in the context of pH measurement?
Why is it important to remove the air inlet cap from a pH electrode before use?
Why is it important to remove the air inlet cap from a pH electrode before use?
What is the recommended method for drying a pH electrode after washing it with distilled water?
What is the recommended method for drying a pH electrode after washing it with distilled water?
Why should a glass electrode be stored in an aqueous solution?
Why should a glass electrode be stored in an aqueous solution?
What should you do if a glass electrode has dried out?
What should you do if a glass electrode has dried out?
What specific pretreatment is advised if an electrode is to be utilized at a reading above a pH of $9$?
What specific pretreatment is advised if an electrode is to be utilized at a reading above a pH of $9$?
What is the primary mechanism by which $H^+$ ions interact with the glass membrane of a pH electrode?
What is the primary mechanism by which $H^+$ ions interact with the glass membrane of a pH electrode?
What is the function of the silver wire coated with $AgCl(s)$ inside a glass electrode?
What is the function of the silver wire coated with $AgCl(s)$ inside a glass electrode?
What is the purpose of the external reference electrode in a potentiometric pH measurement using a glass electrode?
What is the purpose of the external reference electrode in a potentiometric pH measurement using a glass electrode?
What is a key structural characteristic of the silicate glass used in pH electrodes?
What is a key structural characteristic of the silicate glass used in pH electrodes?
Which of the following components is essential for the operation of an ion-selective electrode (ISE) based on a crystal membrane?
Which of the following components is essential for the operation of an ion-selective electrode (ISE) based on a crystal membrane?
What is the role of metal ions such as $Li^+$, $Na^+$, $K^+$, and $Ca^{2+}$ within the silicate glass network of a pH electrode?
What is the role of metal ions such as $Li^+$, $Na^+$, $K^+$, and $Ca^{2+}$ within the silicate glass network of a pH electrode?
What distinguishes an ion-selective electrode (ISE) based on a polymer membrane from one based on a crystal membrane?
What distinguishes an ion-selective electrode (ISE) based on a polymer membrane from one based on a crystal membrane?
In composite electrodes, what is the primary function of the second membrane?
In composite electrodes, what is the primary function of the second membrane?
Which membrane composition is utilized in an ion-selective electrode for fluoride (F-) analysis?
Which membrane composition is utilized in an ion-selective electrode for fluoride (F-) analysis?
What role does the hydrophobic structure surrounding the binding site play in ion-selective electrodes with polymer or liquid membranes?
What role does the hydrophobic structure surrounding the binding site play in ion-selective electrodes with polymer or liquid membranes?
Which of the following components is essential for the function of a liquid membrane ion-selective electrode used for Ca2+ detection.
Which of the following components is essential for the function of a liquid membrane ion-selective electrode used for Ca2+ detection.
Which ionophore is primarily associated with K+ (Potassium) selectivity in ion-selective electrodes?
Which ionophore is primarily associated with K+ (Potassium) selectivity in ion-selective electrodes?
In the context of Ca2+ selective electrodes with liquid membranes, what is the primary purpose of the relatively long aliphatic chains (C8 – C10) attached to the ion exchanger?
In the context of Ca2+ selective electrodes with liquid membranes, what is the primary purpose of the relatively long aliphatic chains (C8 – C10) attached to the ion exchanger?
What is the effect of a low pH environment on a liquid membrane ion-selective electrode used for Ca2+ detection?
What is the effect of a low pH environment on a liquid membrane ion-selective electrode used for Ca2+ detection?
What is the source of interference when measuring $Ca^{2+}$ with the ion selective electrode?
What is the source of interference when measuring $Ca^{2+}$ with the ion selective electrode?
Based on the provided equation, how does the electrode potential (EISE) change with a tenfold increase in $Ca^{2+}$ concentration?
Based on the provided equation, how does the electrode potential (EISE) change with a tenfold increase in $Ca^{2+}$ concentration?
What is a significant limitation of ion selective electrodes when used for analytical measurements?
What is a significant limitation of ion selective electrodes when used for analytical measurements?
When using ion selective electrodes, what is the primary reason for adding a high concentration of an inert salt to both standards and samples?
When using ion selective electrodes, what is the primary reason for adding a high concentration of an inert salt to both standards and samples?
In potentiometry with ion selective electrodes, what is the main reason for eliminating or masking ligands in the sample?
In potentiometry with ion selective electrodes, what is the main reason for eliminating or masking ligands in the sample?
Why is calibration with standard addition particularly useful when working with ion selective electrodes?
Why is calibration with standard addition particularly useful when working with ion selective electrodes?
What is a major advantage of using ion selective electrodes for analysis?
What is a major advantage of using ion selective electrodes for analysis?
Which analytical technique is typically used to measure $pO_2$, exploiting a membrane permeable to oxygen?
Which analytical technique is typically used to measure $pO_2$, exploiting a membrane permeable to oxygen?
Which approach minimizes errors arising from ionic strength differences between samples and standards?
Which approach minimizes errors arising from ionic strength differences between samples and standards?
In potentiometry, if a fraction of the analyte is present in a complex, how does this affect the measurement, and what action should be taken?
In potentiometry, if a fraction of the analyte is present in a complex, how does this affect the measurement, and what action should be taken?
Flashcards
Indicator Electrode
Indicator Electrode
A type of electrode whose potential changes predictably with changes in the analyte concentration.
Metal Indicator Electrode
Metal Indicator Electrode
An electrode whose potential is influenced by a redox reaction involving the analyte.
Ion Selective Electrodes (ISEs)
Ion Selective Electrodes (ISEs)
They work by measuring the difference in analyte concentration between the electrode's internal solution and the sample being analyzed.
Metal Indicator Electrode Response
Metal Indicator Electrode Response
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ISE Response Mechanism
ISE Response Mechanism
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Metal Electrode Limitations
Metal Electrode Limitations
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ISE Advantages
ISE Advantages
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ISE Response to Charge
ISE Response to Charge
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Silver-Silver Chloride (Ag/AgCl) Reference Electrode
Silver-Silver Chloride (Ag/AgCl) Reference Electrode
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Half-Reaction of the Ag/AgCl Electrode
Half-Reaction of the Ag/AgCl Electrode
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Electrode Potential of the Ag/AgCl Electrode
Electrode Potential of the Ag/AgCl Electrode
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Internal Solution of the Ag/AgCl Electrode
Internal Solution of the Ag/AgCl Electrode
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Calomel Reference Electrode
Calomel Reference Electrode
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Saturated Calomel Electrode (SCE)
Saturated Calomel Electrode (SCE)
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Interferents for the Ag/AgCl Electrode
Interferents for the Ag/AgCl Electrode
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Double Junction Reference Electrode
Double Junction Reference Electrode
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Glass Electrode
Glass Electrode
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Ion-Selective Electrode (ISE)
Ion-Selective Electrode (ISE)
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Glass Membrane
Glass Membrane
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Potentiometry
Potentiometry
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Internal Reference Electrode
Internal Reference Electrode
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External Reference Electrode
External Reference Electrode
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Silicate Glass Structure
Silicate Glass Structure
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Hydrated Gel Regions
Hydrated Gel Regions
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pH meter
pH meter
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pH standard buffer
pH standard buffer
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Thermal probe
Thermal probe
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Temperature effect on pH
Temperature effect on pH
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Temperature effect on electrode response
Temperature effect on electrode response
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pH meter calibration
pH meter calibration
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Automatic Temperature Compensation (ATC)
Automatic Temperature Compensation (ATC)
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LaF3 Crystal Doped Ion Selective Electrode
LaF3 Crystal Doped Ion Selective Electrode
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What are ion-selective electrodes (ISEs)?
What are ion-selective electrodes (ISEs)?
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How do polymer or liquid membrane ISEs work?
How do polymer or liquid membrane ISEs work?
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What's the role of the ionophore in ISEs?
What's the role of the ionophore in ISEs?
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Examples of ionophores
Examples of ionophores
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What are ionophores used for?
What are ionophores used for?
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Specific ionophores for calcium and sodium
Specific ionophores for calcium and sodium
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How does a liquid membrane ISE for Ca2+ work?
How does a liquid membrane ISE for Ca2+ work?
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Selectivity of ISEs
Selectivity of ISEs
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Limitations of ISEs: Precision
Limitations of ISEs: Precision
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Limitations of ISEs: Contamination
Limitations of ISEs: Contamination
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Limitations of ISEs: Complexation
Limitations of ISEs: Complexation
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Limitations of ISEs: Ionic Strength
Limitations of ISEs: Ionic Strength
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Standard Addition Method for Calibration
Standard Addition Method for Calibration
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Study Notes
Potentiometry
- Potentiometry is an electrochemical analytical technique that measures voltage in an electrochemical cell to determine the concentration of chemical species.
- Electrodes, specifically ion selective electrodes, enable rapid, sensitive, and selective measurements. Measurements are performed using laboratory or portable instruments.
- Electric rays and other fishes, generate strong electric shocks using electric organs. Nerve terminals rapidly release acetylcholine to cause sodium ions to surge through membranes, generating a voltage across the membrane. Human technology is inspired by this process.
Introduction
- Electricity can be used to power chemical reactions, and vice-versa, chemical reactions can be used to create electricity in potentiometry.
- Electric charge is measured in Coulombs (C). The flow of charge is balanced: negative charge flow is countered by positive charge flow.
- Electric potential difference (voltage) is the work per unit charge. Current (I) is the rate of charge flow (1A = 1C/s).
Electrochemical Cells
- Electrochemistry uses electrical measurements to study chemical systems. Electrochemical cells contain two half cells joined by a salt bridge.
- Ions flow to oppositely charged electrodes. Electrons flow between electrodes and an external circuit.
- The potential difference, or voltage, is measured between electrodes using a potentiometer which has high resistance to limit current flow.
Standard Potentials
- Standard potential (E°) shows the driving force for redox reactions under standard conditions (all species have activity=1 and a reference electrode is used).
- Redox reaction refers to the transfer of electrons between species.
- Specific half-cell reactions have their own characteristic E° values. These dictate their behaviour as either cathodes or anodes.
Nernst Equation
- The Nernst equation relates the cell potential (E) to the concentrations of reactants. It accounts for activities (better said concentrations) of the involved species in a chemical reaction.
- The reaction quotient (Q) in the equation shows the relative ratio of product and reactant concentrations. At equilibrium, Q=K, leading to E=0
Reference Electrodes
- Reference electrodes maintain stable potentials, independent of the analyte being measured.
- Commonly used reference electrodes use a metal and its corresponding insoluble salt. E.g. AgCl/Ag.
- The potential depends on the concentration of the anion that forms the insoluble salt with the metal, and in most cases, a known solution with high concentration of the anion (e.g., KCl in a saturated solution) is used for this purpose.
Indicator Electrodes
- Indicator electrodes (often called working electrodes) respond to variations on the analyte concentration.
- Metal indicator electrodes show their response based on a redox reaction involving the analyte.
- Ion selective electrodes (ISEs) do not use redox reactions. They respond based on selective interaction between the analyte and a membrane. The difference in analyte concentration inside the electrode and in external solution is measured.
pH Measurement with Glass Electrodes
- Glass electrodes are the most common ion selective electrodes for pH measurements. The electrode measures the potential difference between an internal reference electrode and an external analyte solution using a glass membrane.
- The internal reference is fixed (e.g H+), so potential variations depend entirely on the analyte solution pH. This makes pH readily measurable when using glass electrodes.
pH Combination Electrode
- pH combination electrodes combine both a glass electrode and a reference electrode in a single unit.
- The reference electrode is typically a silver-silver chloride electrode that provides a stable reference potential.
Errors in pH Measurements with Glass Electrodes
- Standards: pH measurements depend on the accuracy of known buffers.
- Junction potential: the potential difference at the junction between the probe's internal and external solutions, can influence the result, but it is usually stable with well buffered solutions.
- Temperature effects: temperatures variations affect the pH measurement as well as the calibration standards, thus, precise calibration at the same temperature as the sample is needed.
Ion Selective Electrodes for Other Ions
- Many other ISEs are available for measuring various ions. These include modified composition glass electrodes with varying compositions or crystalline, polymer, or liquid membranes and ion exchangers.
- Methods like standard addition or saturation can be implemented to mitigate errors related to the differences between the sample and standards ionic strength.
Potentiometric Gas-Sensing Probes
- Probes for gases like CO2 can be used to measure gas concentrations.
- They use a membrane that is selectively permeable to the target gas, which causes a pH change in the inside solution, detected by a glass electrode.
Use of Ion Selective Electrodes
- ISEs allow for non-destructive analysis using fast and direct measurements on many different ions.
- They can be used in turbid or coloured solutions, avoiding the need for complex sample preparation.
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Description
Test your knowledge on the Ag/AgCl reference electrode and its properties. This quiz covers standard reduction potentials, concentration effects, and the characteristics of effective indicator electrodes. Dive into the fascinating world of electrochemistry and enhance your understanding of reference electrodes.
