| Home » Chemistry Homework Help » Physical Chemistry » Junction Potentials |
Junction Potentials
If the electrode solutions are different, the end of the cell includes a junction potential.
The treatment of emf’s so far has ignored the problem that arises if one seeks to couple two electrodes which operate in different solutions. If, for instance, one studies the cell consisting of a Zn|Zn2+ electrode and a Cu | Cu2+ electrode, one must separate the two solutions, perhaps solutions containing ZnSo4 and CuSO4, so that they cannot mix with each other. Since the direct contact between solutions of different concentrations is not a balanced state, as required for reversible processes, the system is not directly susceptible to thermodynamic analysis.
The dilution of HCl was studied very comprehensibly. Assume that two HCl solutions of different concentrations can be brought together and prevented from mixing. The flowing of two streams of solution together sometimes accomplishes this. One can set up the cell:
Pt | H2 | HCl (c1) |H2|Pt
The emf of the cell can be related to the overall reaction that occur when 1 mol of current flows. The reactions which occur at the electrodes and those which occur at the liquid junction can be written separately. The electrodes reactions are:

The emf of this cell, which has Ø˚ = 0, can be written,
Ø˚ = - 0.05915/1 log [(aH+) 1 9aC1-) 1]t-/ [(aH+)2 (aC1-)2]t- = - 0.05915t- log [a±]21/[a±]22
The emf of the cell, unlike that without a liquid junction, depends on the transference numbers. Such cells are frequently described as concentration cells and transference.
If the activities of HCl at the two concentrations are known, the measured emf allows the determination of the transference number. The method is satisfactory and the results compare well with those obtained by the Hittorf method. The difficulties with the method arise through the experimental problem of obtaining a liquid junction that prevents mixing of two solutions. Reproducible and meaningful emf’s are always easily obtained. The assumption has been made furthermore, that the transference numbers are independent of concentration in the concentration range of c1 to c2
Example: the emf of the following concentration cell with transference was studied.
Ag | AgCl | NaCl (aq, c1) | NaCl (aq, c2) | AgCl | Ag
The temperature was kept at 25˚C, and for each of the cells studied the value of c1 was 0.0498 mol L-1. The activity coefficient γ ± of NaCl in this solution is 0.0823.
Here are some of the results obtained in a study by J. Janz and A. R. Gordon, J, Am. Chem. Soc., 65:218 (1943).

Show that this emf’s can be accounted for by a transference number t+ of 0.39 over this concentration range.
Solution: the electrode reactions are:

The cell also involves junction reactions:
Junction reactions can also be described, since t+ = 1 – t-, as
t+NaCl (aq, c1)
t+ (NaCl aq, c2)
Cl- (aq, c1)
Cl- (aq, c2)
The net cell reaction, the sum of the electrode and the junction processes, is:
Cell reaction: t+ NaCl (aq, c1)
t+ NaCl (aq, c2)
The cell emf, with δ˚ = 0, is
δ = -0.05915 log [(a ±)22]t+/[a ±)21]t+

Services:- Junction Potentials Homework | Junction Potentials Homework Help | Junction Potentials Homework Help Services | Live Junction Potentials Homework Help | Junction Potentials Homework Tutors | Online Junction Potentials Homework Help | Junction Potentials Tutors | Online Junction Potentials Tutors | Junction Potentials Homework Services | Junction Potentials
The treatment of emf’s so far has ignored the problem that arises if one seeks to couple two electrodes which operate in different solutions. If, for instance, one studies the cell consisting of a Zn|Zn2+ electrode and a Cu | Cu2+ electrode, one must separate the two solutions, perhaps solutions containing ZnSo4 and CuSO4, so that they cannot mix with each other. Since the direct contact between solutions of different concentrations is not a balanced state, as required for reversible processes, the system is not directly susceptible to thermodynamic analysis.
The dilution of HCl was studied very comprehensibly. Assume that two HCl solutions of different concentrations can be brought together and prevented from mixing. The flowing of two streams of solution together sometimes accomplishes this. One can set up the cell:
Pt | H2 | HCl (c1) |H2|Pt
The emf of the cell can be related to the overall reaction that occur when 1 mol of current flows. The reactions which occur at the electrodes and those which occur at the liquid junction can be written separately. The electrodes reactions are:
The emf of this cell, which has Ø˚ = 0, can be written,
Ø˚ = - 0.05915/1 log [(aH+) 1 9aC1-) 1]t-/ [(aH+)2 (aC1-)2]t- = - 0.05915t- log [a±]21/[a±]22
The emf of the cell, unlike that without a liquid junction, depends on the transference numbers. Such cells are frequently described as concentration cells and transference.
If the activities of HCl at the two concentrations are known, the measured emf allows the determination of the transference number. The method is satisfactory and the results compare well with those obtained by the Hittorf method. The difficulties with the method arise through the experimental problem of obtaining a liquid junction that prevents mixing of two solutions. Reproducible and meaningful emf’s are always easily obtained. The assumption has been made furthermore, that the transference numbers are independent of concentration in the concentration range of c1 to c2
Example: the emf of the following concentration cell with transference was studied.
Ag | AgCl | NaCl (aq, c1) | NaCl (aq, c2) | AgCl | Ag
The temperature was kept at 25˚C, and for each of the cells studied the value of c1 was 0.0498 mol L-1. The activity coefficient γ ± of NaCl in this solution is 0.0823.
Here are some of the results obtained in a study by J. Janz and A. R. Gordon, J, Am. Chem. Soc., 65:218 (1943).
Show that this emf’s can be accounted for by a transference number t+ of 0.39 over this concentration range.
Solution: the electrode reactions are:
The cell also involves junction reactions:
Junction reactions can also be described, since t+ = 1 – t-, as
t+NaCl (aq, c1)
Cl- (aq, c1)
The net cell reaction, the sum of the electrode and the junction processes, is:
Cell reaction: t+ NaCl (aq, c1)
The cell emf, with δ˚ = 0, is
δ = -0.05915 log [(a ±)22]t+/[a ±)21]t+
Services:- Junction Potentials Homework | Junction Potentials Homework Help | Junction Potentials Homework Help Services | Live Junction Potentials Homework Help | Junction Potentials Homework Tutors | Online Junction Potentials Homework Help | Junction Potentials Tutors | Online Junction Potentials Tutors | Junction Potentials Homework Services | Junction Potentials
Submit Your Query ???
Assignment Help
Inorganic Chemistry
Organic Chemistsry
Analytical Chemistry
Biochemistry
Physical Chemistry
Topics
Covalent Radii
Crystal Shapes, Point Groups
Diffraction Pattern Assignments
Electron Diffraction
Ionic Radii
Lattice Energies
Diffraction
Lattices, Unit Cells
Neutron Diffraction
Waals Radii
X-ray Diffraction
Bond Moments
Electric Capacitor
Atoms, Molecules Properties
Paramagnetism
Electrolytic Dissociation
Solution Ionic Strength
Solvent Dielectric Effect
Electrolysis
Solutions Ionic Mobilities
Electrolytes In Solutions
Solutions Molar Conductance
Solutions Specific Conductance
Electrochemical Cell EMF
Electrodes
Ion Selective Electrodes
Junction Potentials
Cells Electromotive Force
Standard Electrode Potentials
Collision Theory
Gas Viscosity Theory
Elementary Reactions
Lasers
Molecule-Molecule Collisions
Electrochemical Cell
Photochemical Quenching
Surface Decompositions
Atomic Molecular Energies
Molecular Energies
Particle-in-a-box
Particle-on-a-line
Rotational Energies
Schrodinger Wave Equation
De Broglie Wave Length
Vibrational Energies
Waves And Particles
Boltzmann Distribution
Gas Heat Capacities
Metals Heat Capacities
Molecules Collection Energies
One Dimensional Motion
Partition Function
Rotational Motions
Thermal Energy
Three Dimensional Motion
Vibrational Motions
Aqueous Ion Energies
Bond Energies
Chemical Systems Energy
Enthalpy, Chemical Reactions
Chemical System Enthalpy
Thermodynamics First Law
Heat Capacities
Thermodynamics
Molecular Thermal Energy
Standard Enthalpy Substance
Carnot Cycle
Absolute Zero Entropies
Entropy
Thermodynamics Laws
Entropy Molecular Basis
Third Law Molecular Basis
Rotational Energy
Thermodynamics Second Law
Thermodynamics Third Law
Vapourization Entropy
Vibrational Entropy
Equilibria And Distributions
Real Gases Equilibria
Free Energy Equilibrium Constant
Free Energy And Pressure
Free Energy, Temperature
Free Energy Function
Free Energy Real Gases
Free Energy
Fugacity
Non-ideal Gases Fugacity
Thermodynamic Properties
Chemical Equilibria
Boyle Gas Pressure
Continuity Of States
Critical Point
Gas Mixtures
Kinetic Molecular Theory
Gases-Properties, Theories
Molecular Energies, Speed
Molecular Interactions
Real Gas PVT
Temperature Volume
Waals Gases Behaviour
Waals Critical Point
Molecular Diameters
Virial Equation
Diffusion Coefficient
Diffusion Molecular View
Donnan Membrane Equilibria
Electrophoresis
Macromolecular Dynamics
Average Mass Range
Solution Viscosity
Sedimentation And Velocity
Colloids Macromolecules Micelles
Adsorption Isotherm
Adsorption Of Gases
Boiling Point Diagrams
Pressure Temperature Relation
Distillation
Eutectic Formation
Immiscible Liquids
Phase Equilibria
Liquid Surfaces
Phase Rule
Pressure Phase Diagrams
Solid Compound Foundation
Surface Tension Vapour Pressure
Three Component System
Vapour Pressure Composition
Atomic States
Bohr Atom
Electron Spin
Angular Momentum Hydrogen
Hydrogen Atom Spectra
Hydrogen Radical Factor
Quantum Atomic Structure
Quantum Mechanical Operators
Variation Theorem
Enzymes Catalyzed Reactions
First Order Rate Equations
Flash Photolysis
Chemical Reactions Mechanism
Enzyme Reactions Mechanism
Reactions Mechanisms
Photochemical Reactions
Rate Equation
Second Order Rate Equations
Temperatures And Rates
Unimolecular Gas Reactions
Absorption Coefficient
Einstein Coefficient
Electromagnetic Induction
Electronic Spectra
Electron Spin Spectroscopy
Infrared Adsorption
Spectroscopy
Microwave Absorption
Nuclear Spin States
Nuclear Magnetic Resonance
Photoelectron Spectroscopy
Polyatomic Vibrational Spectra
Rotational Vibrational Spectra
Conjugated Systems Spectra
Transition Moment
Character Tables
Symmetry Group Theory
Molecular Symmetry Types
Orbital Symmetries
Point Groups
Reducible Representation
Symmetry Elements, Operations
Molecular Properties Symmetry
Transformation Matrices
Diatomic Molecule Orbitals
Electronegativity
Hybridization
Hydrogen Molecule Ion
Ionic Bond
Molecular Orbitals
Orbitals Pie Electrons
Two Electron Bond
Virial Theorem
Partial Molal Properties
Solute Free Energy
Ideal Mixtures
Solution Thermodynamic Property
Liquid Vapour Free Energies
Osmotic Pressure
Partial Molal Quantities
Solvent Free Energy
Vapour Pressure Lowering




Homework Help, Online Tutor, Online Tutoring Available For All Subjects. Some useful topics are given below :