a measure of efficiency of an electrolyte to conduct electricity of a solution
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molar conductivity equation and units
^= k/c (S m2mol-2)
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definition of electrolyte
any substance that dissociates into ions when dissolved, thus conducting electricity.
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ionic strength equation
I = 1/2ΣCZ^2. C-conc of ion Z-charge of ion
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activity definition and equation
"the effective concentration of a solution" a=YC a-activity y-activity coefficient C-concnetration Logy± =-0.5[Z+Z-]√I I-ionic strength.
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what is potentiometry
reversible electrode potential, potential at liquid/solid interphase. final potential depends on position of equilibrium- equilibrium depends on activity so all depends on the potential.
net migration foils from high to low conc, there's a build up of charge on one side of the salt bridge, pick the material to minimuse this charge.
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Nernst equation
Ecell = E*cell -2.303RT/nF. logC
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traits of a reference electrode in potentiometry
should not drift,(potential remains constant) reproducible, easy to assemble
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3 examples of reference electrodes in potentiometry
SHE- zero at all temps, H2 flammable Pt Calomel- HCl/Hg2Cl2/Hg Hg2Cl2 +2e--> 2Hg + 2 Cl. Silver/Silverchloride KCl/AgCl/Ag. AgCl +e -> Ag(s) + Cl-
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indicator electrodes in potentiometry
develop a potential due to redox at the surface. electrodes are there to transmit to and from species in solution.
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explain ion selective electrodes
don't depend on redox processed, ion selective membrane, only certain analyze can cross, when membrane is put in the solution two interfaces are made. the potential differences between these interfaces.
increasing potential applied between working and counter electrode. the current that flows is measured. the current flowing is proportional to concentration. working e must be polarizable counter electrode non polarizable.
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explain concentration gradient in voltometry
reaction only happens at electrode, a concentration gradient forms between surface of electrode and bulk of the rest fo the solution
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3 mass transfer processes
migration- movement of charged particles in electric field-bad drown out with excess electrolyte. Convection, due to thermal gradient and stirring bad. diffusion, concentration radiant-good can be made reproducible.
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voltometry problem charging current
electrical double layer forms at the electrode acts as a storage charge, current is needed to polarize this, use microelectrode to decrease this current needed.
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reference electrode in voltometry
used to measure potential of working electrode, current doesn't pass through this
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counter electrode in voltometry
allows current to be passed through the cell, if theres oxidation at working e reduction will be at counter electrode.
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what is amperometry
measurement of current flow resulting from a redox reaction, using.a constant potential at the working electrode. the current flow is directly proportional to conc.
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