3B Scientific Electrochemistry Kit - Manual (Page 7)

8
Experiment 1 - Measuring voltage Teacher's instructions
Measuring the voltage of galvanic cells - teacher's instructions
Chemicals Hazard
symbols
R phrases S phrases Equipment
Copper (II)-sulfate-(5 H
2
O) 22-36/38-50/53 22-60-61 Meter
Zinc sulfate-(7H
2
O) 36/38-50/53 22-25-60-61 Electrodes:
1 Cu, 1 Zn,1 Ag, 1 Fe, 1 Ni
Silver nitrate 34-50/53 26-45-60-61 2 Experiment cables
Iron (II)-sulfate-(7 H
2
O) 22-36/38 24/25 2 Pipettes
Nickel sulfate-(6H
2
O) 22-40-42/43-
50/53
22-36/37-60-
61
Distilled water --- ---
Warning: Please take care: Salts of heavy metals are poisonous!
Experiment procedure:
1. The prepared 1.0 and 0.1 molar electrolyte solutions should be given to the students. Students require no more than
10 ml of the relevant solution each.
2. Assemble the battery block as described.
3. Fill the chambers with electrolyte using the pipette (included in the case) and insert the appropriate electrodes.
Clean the pipette thoroughly before using it add the next electrolyte.
4. After the chambers (at least 2, at most 8) have been prepared for the experiment as described, start measuring
voltages. In this experiment, each of 5 chambers is filled with a separate electrolyte and
the corresponding electrode is inserted to make up a galvanic cell:
Cu / CuSO
4
, Zn / ZnSO
4
, Ag / AgNO
3
, Fe / FeSO
4
, Ni / NiSO
4
5. To measure voltage, two experiment cables (red/blue with 2mm plugs - included in case) should be connected to the
voltmeter. The connection between the two electrodes and the meter is made by means of crocodile clips.
6. The voltage produced by the galvanic cell can be read off the meter. If a negative voltage is displayed, reverse the
polarity of the two electrodes.
Observation and evaluation:
In galvanic cells, the less electropositive metal always forms the negative pole.
Electrons always flow from negative to positive poles, i.e. for a zinc/copper combination, they flow from the zinc to the copper and in a
copper/silver combination, they flow from copper to silver.
The combinations involving zinc always have zinc as the negative pole and those involving silver always have silver as the positive pole
of the galvanic element. An electrochemical potential series for these metals thus has the following order:
Zn
→
Fe
→
Ni
→
Cu
→
Ag
Which of the electrodes forms the negative pole can be determined by reversing the polarity.
Galvanic cell Voltage (V)
Electrolyte 1.0 mol/l
Voltage (V)
Electrolyte 0.1 mol/l
Cu / Zn 1.086 approx. 1.086 approx.
Cu / Ag 0.383 approx. 0.383 approx.
Cu / Fe 0.670 approx. 0.670 approx.
Cu / Ni 0.044 approx. 0.044 approx.
Zn / Ag 1.416 approx. 1.416 approx.
Zn / Fe 0.378 approx. 0.378 approx.
Zn / Ni 1.095 approx. 1.095 approx.
Fe / Ag 1.089 approx. 1.089 approx.
Fe / Ni 0.700 approx. 0.700 approx.
Ag / Ni 0.290 approx. 0.290 approx.
Calculation of masses required to prepare a 0.1 molar solution:
The electrolyte solutions should be made up by the teacher in sufficient quantities (usually 1 liter suffices) in advance of the lesson.
1.
1 liter of 1.0 molar CuSO
4
solution: Add water to 249.50 g CuSO
4
(5 H
2
O) up to 1 liter in a measuring flask.
2. 1 liter of 1.0 molar ZnSO
4
solution: Add water to 287.40 g ZnSO
4
(7 H
2
O) up to 1 liter in a measuring flask.
3. 1 liter of 1.0 molar AgNO
3
solution: Add water to 169.88 g AgNO
3
up to 1 liter in a measuring flask.
4. 1 liter of 1.0 molar FeSO
4
solution: Add water to 277.90 g FeSO
4
(7 H
2
O) up to 1 liter in a measuring flask.
5. 1 liter of 1.0 molar NiSO
4
solution: Add water to 262.70 g NiSO
4
(6 H
2
O) up to 1 liter in a measuring flask.
To make up a 0.1 molar solution, simply use 1/10 of the quantities given above (for making a 1.0 molar solution)
and add water up to 1 liter in a measuring flask.