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Chemistry Experiment no 7 (STPM BAHARU)
Topic : ElectrochemistryFaradays Laws
Purpose : To determine the value of Avogadros constant by the electrolysis
procedure.
Theory : Faradays First law states that the mass of a substance produced at an
electrode during electrolysis is directly proportional to the quantity of
electricity (in Coulombs) passed.
Faradays Second law states that the number of moles of a substance
produced at an electrode during electrolysis is inversely proportional to
the charge on the ion. The number of Faradays required to discharge one
mole of an ion at an electrode equals to the charge on the ion.
Apparatus : (a) One 250cm beaker.
(b) One set of battery.
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(c) One ammeter.
(d) One rheostat.
(e) Some connecting wires with crocodile clips.
(f) One stop watch.
(g) One hair dryer.
(h) One piece of sandpaper.
(f) One wash bottle filled with distilled water.
Materials : 200cm aqueous copper(II) sulphate solution.
2 pieces of copper plates.
Propanone solution.
Procedure : 1. Two copper plates are cleaned with sandpaper. Then, it is washed with
distilled water and propanone. It is dried by using hair dryer.
2. The mass of copper plates is measured and recorded.
3. The apparatus is arranged as shown as figure 1. The ammeter reading
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( 1.0 A) is fixed.
4. The copper plates are dipped into aqueous copper(II) sulphate solution
and switched on.
5. After 20 minutes, the copper plates are removed. It is washed with distilled water and
dried it. Its mass is measured and recorded
Results : (b) The readings are recorded and the table below is completed.
Initial mass/g Final mass/g Mass /g ( Final- Initial)
Copper at anode 1.58 1.76 0.18
Copper at cathode 1.52 1.32 -0.20
Calculation :
Current , I = 0.5A
Time, s = 20 x 60 = 1200s
Quantity of electricity passed through, Q = It
= 0.5 x 1200
= 600C
Mass of copper = ( 0.18 + 0.20 )
2
= 0.19g
Relative atomic mass of copper, Cu = 63.5g
Number of mole of copper, Cu = 0.19
63.5
= 2.99 x 10 mol
Cu (s) Cu (aq) + 2e
1 mol of copper = 2 mol of electrons
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Number of Faraday required = 2
2F = 600
2.99x10
F = 1.00 x 10 C mol
F = Le
= 1.00 x 10
1.60 x 10
= 6.23 x 10 mol
Conclusion :The real Avogadros constant is 6.02 x 10 but the experimental
Avogadros constant is 6.23 x 10.
Comment :The reading is slightly different from the value on theory. There are
some parallax error when the experiment is carried on.