Temperature dependence of the electromotive force

The electromotive force is the potential
difference of the single potentials
of the according electrodes in a
galvanic chain. It is equal to the difference
of all the single potentials
which can be calculated using the
Nernst equation. Thermodynamic
data of the gross reaction in a galvanic
chain can be determined measuring
the e.m.f. at different temperatures.
The usable reaction equivalent work
of the Daniell element is determined
by measuring the dependence of the
electromotive force on temperature.
Related concepts
Electromotive force, electrode reactions, electrochemical potential,
Nernst equation.
Principle
Thermodynamic data of the gross reaction in a galvanic cell can
be determined by measuring the e.m.f. at different temperatures.
Tasks
Determine the usable reaction equivalent work of the Daniell cell
by measuring the dependence of the electromotive force on
temperature.
Prepare the solutions required for the experiment as follows:
– 1 molar CuSO4 solution: Weigh 62.420 g of copper(II) sulphate
(CuSO4•5H2O) into a 250 ml volumetric flask, dissolve
it in distilled water, and make up to the mark with distilled
water.
– 1 molar ZnSO4 solution: Weigh 71.8920 g of zinc sulphate
(ZnSO4•7H2O) into a 250 ml volumetric flask, dissolve it in
distilled water, and make up to the mark with distilled water.
– 1 molar KNO3 solution: Weigh 25.276 g of potassium nitrate
into a 250 ml volumetric flask, dissolve it in distilled water,
and make up to the mark with distilled water.
– Saturated KNO3 solution: Weigh 20 g of potassium nitrate
into a 150 ml beaker, add 50 ml of distilled water and stir for
some minutes at room temperature. Some potassium nitrate
must remain on the bottom of the beaker in the solid state. If
this is not the case, additional potassium nitrate must be
added. When the undissolved potassium nitrate has settled,
decant the saturated solution into a second beaker.
Soak the clay pins in saturated potassium nitrate solution
overnight.
Place the two half-cells (150 ml beakers) together in the bath of
the immersion thermostat. Fill one beaker with 1 molar copper
sulphate solution and the other with 1 molar zinc sulphate solution.
The level of the liquids in the beakers should be equal and
not higher than the surrounding water in the bath of the thermostat.
Use a syringe with a cannula to carefully fill the salt bridge with
1 molar potassium nitrate solution. Remove air bubbles by tapping
at the arms of the salt bridge. Seal each arm of the salt
bridge with a soaked clay pin which is held in place by a short
length (20 mm) of silicone tubing. Replace the cap. For every
new series of measurement a new pair of clay pins must be used
because electrode reactions are extremely sensitive to impurities.
Immerse the salt bridge in the two beakers to connect both
solutions.