19.1 standard electrode potentials - mattlidens gymnasium · of only one half-cell, standard...
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● In a voltaic cell electrons flow from the half-cell with a more negative potential to the half-cell with a more positive potential and generates an electromotive force (emf).
● The magnitude of the voltage depends on the difference in the tendencies of the two half-cells to undergo reduction.
19.1 Standard electrode potentials
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● Since it is impossible to measure the electrode potential of only one half-cell, standard hydrogen electrode is used as a reference electrode.
● It is assigned a standard electrode potential of 0,00 V.
● Standard conditions:
● all solution must be 1.0 mol dm-3
● 100 kPa● all substances are pure● 298K● solid metals or Pt as an electrode
2 H+(aq) + 2e- H2(g)
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● The standard electrode potential of a half-cell is determined by connecting that half-cell to the standard hydrogen electrode at standard conditions and measuring the e.m.f .
Zn (s) | Zn2+ (1 M) || H+ (1 M) | H2 (1 atm) | Pt (s)
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● The sign of the standard electrode potential depends on the direction of electron flow:
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● Standard electrode potentials are always given for the reduction reaction.
● The E° values for the oxidation will be of equal magnitude but have the opposite sign.
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● In a spontaneous reaction the half-cell with the more negative standard electrode potential gives up electrons = is oxidised whereas the half-cell with the more positive standard electrode potential recieves electrons = is reduced.
= The electrons flow towards the half-cell with the highest Eº value.
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Electrolysis of aqueous solutions
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Electrolysis of a concentrated solution of NaCl (aq)
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Electrolysis of CuSO4 (aq) using inert graphite electrodes
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Electrolysis of CuSO4 (aq) using copper electrodes
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How much Ca will be produced in an electrolytic cell of molten CaCl2 if a current of 0.452 A is passed through the
cell for 1.5 hours?