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What is a limitation of conductometric determinations?
What is a limitation of conductometric determinations?
What is the purpose of a reference electrode in potentiometry?
What is the purpose of a reference electrode in potentiometry?
What happens when a metal of high solution pressure is immersed in a solution of its ions?
What happens when a metal of high solution pressure is immersed in a solution of its ions?
What is the sign of the EMF produced when a metal of high solution pressure is immersed in a solution of its ions?
What is the sign of the EMF produced when a metal of high solution pressure is immersed in a solution of its ions?
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What is the equation used to calculate the electrode potential?
What is the equation used to calculate the electrode potential?
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What is the relationship between the electrode potential and the ionic concentration?
What is the relationship between the electrode potential and the ionic concentration?
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What is the role of the indicator electrode in potentiometry?
What is the role of the indicator electrode in potentiometry?
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What happens when a metal of high ionic pressure is immersed in a solution of its ions?
What happens when a metal of high ionic pressure is immersed in a solution of its ions?
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What is the sign of the EMF produced when a metal of high ionic pressure is immersed in a solution of its ions?
What is the sign of the EMF produced when a metal of high ionic pressure is immersed in a solution of its ions?
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What is the purpose of potentiometry?
What is the purpose of potentiometry?
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Study Notes
Electrodes Classification
- Electrodes are classified into two classes:
- Electrodes where redox reaction (electron transfer) takes place at electrode surface, e.g. metallic electrodes
- Electrodes where charge (ions) exchange takes place at specific membrane surface, e.g. ion selective electrodes (or specific ion electrodes)
Indicator Electrodes
- Indicator electrodes used for different reactions:
- Electrodes used for redox reactions:
- Inert electrodes that acquire the potential of the system in which they are dipped
- Examples: platinum or gold in the form of coils or foils or plates to expose a large surface area to the solution
- Electrodes used for precipitimetry and complexometry:
- Electrodes of first type (Kind or order):
- Examples: Ag° for determination of Ag+, Cu, Pb, Cd, and Hg
- Potential: EAg° = Eo + 0.059 log [Ag+]
- Electrodes of second type:
- Used for determination of anions
- Examples: Ag° coated with a layer of AgCl immersed in Cl- sample
- Potential: EAg° = Eo - 0.059 log [Cl-]
- Electrodes of first type (Kind or order):
- Electrodes used for neutralisation reactions:
- Hydrogen electrode
- Antimony electrode
- Advantages: easy to use, cheap, and durable
- Disadvantages: can't be used in presence of oxidising and reducing agents, and only used between pH 2-8
- Electrodes used for redox reactions:
Standard Electrode Potential
- Standard electrode potential is the EMF produced when a metal is immersed in 1 M solution of its ions
- Eo is a quantitative measure of readiness of metal to lose electrons or gain electrons by non-metal giving its ions
- The sign of the potential is similar to the charge on the metal electrode
Electrochemical Cells
- Galvanic cells:
- Voltalic cell: Zn°/ Zn2+// Cu°/ Cu2+
- Concentration cell:
- Each half cell contains the same metal and its ions, but the concentration of metal ion is different
- Produces EMF of the cell
- Salt bridge:
- Permits the passage of electric current between the solutions present in the electrodes
- Liquid junction potential:
- Developed between the two boundaries of the junction at the two ends of the salt bridge
- Produced due to the difference in the rates of migration of both cations and anions of the salt bridge
- To reduce liquid junction potential, choose the electrolyte of the salt bridge that its cations and anions have nearly the same mobility
Potentiometry
- Potentiometry is a method of analysis concerned with the determination of an ion by dipping a suitable sensor in its solution
- The potential of the indicator electrode is measured relative to a reference electrode possessing a constant potential
- The concentration of the ion is determined using the Nernst equation
- When a rod of metal is dipped in a solution of its ions, it may have:
- Tendency to lose electrons and convert to its ions (high solution pressure)
- Tendency of metal ion to accept electrons and convert to element (high ionic pressure)
- Calculation of electrode potential:
- E25°C = Eo + 0.059 log [Mn+] (Nernst equation)
- Where: E25°C = electrode potential at 25°C, Eo = standard electrode potential, n = number of electrons gained or lost, [Mn+] = molar concentration of metal ion
- E25°C is a function of ionic concentration
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Description
This quiz covers the classification of electrodes into two types, including metallic electrodes and ion selective electrodes, and their uses in different reactions.
