3B Scientific Electrochemistry Kit - Manual (Page 13)

14
Experiment 4 - Measuring voltage Teacher's instructions
Measuring the voltage of three Daniell cells connected in series
Chemicals Hazard
symbols
R phrases S phrases Equipment
Meter
Copper (II)-sulfate-(5 H
2
O) 22-36/38-50/53 22-60-61 Electrodes:
3 Cu, 3 Zn
Zinc sulfate-(7H
2
O) 36/38-50/53 22-25-60-61 4 Experiment cables
Distilled water --- --- 2 Pipettes
Warning: Please take care: Salts of heavy metals are poisonous!
Experiment procedure:
1. The prepared 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 three chambers on one side of the battery block with 0.1 molar CuSO
4
solution then insert the copper electrodes.
4. Now fill three chambers on the other side of the battery block with 0.1 molar ZnSO
4
solution then insert the zinc
electrodes.
5. Connect two copper electrodes to two zinc electrodes using experiment cables with crocodile clips and then connect
the last copper and the last zinc electrode to the meter.
6. Read off the voltage from the meter.
(If a negative value is displayed on the meter, reverse the polarities of the cables to the meter.)
Observation and evaluation:
Sketch of experiment set-up:
Cu
+ +
Meter
-
Zn
In the series circuit, the measured voltage with three electrodes connected together should be V= 3.18 V approx. It can be seen that
connecting the electrodes in series leads to an increase in voltage proportional to the number of cells connected. The current that flows
in this case is no higher than for the basic arrangement.
If a higher voltage is required, this can only be achieved by connecting cells in series.
The electrolyte solutions should be made up by the teacher in sufficient quantities (usually 1 liter suffices) in advance of the lesson.
Calculation of masses required to prepare a 0.1 molar solution:
1.
1 liter of 0.1 molar CuSO
4
solution: Add water to 24.95 g CuSO
4
(5 H
2
O) up to 1 liter in a measuring flask.
2. 1 liter of 0.1 molar ZnSO
4
solution: Add water to 28.74 g ZnSO
4
(7 H
2
O) up to 1 liter in a measuring flask.