7/30/2019 Chemistry Experiment No 7

1/4

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.

7/30/2019 Chemistry Experiment No 7

2/4

(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

7/30/2019 Chemistry Experiment No 7

3/4

( 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

7/30/2019 Chemistry Experiment No 7

4/4

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.