3B Scientific Electrochemistry Kit - Manual (Page 11)

12
Experiment 3 - Measuring voltage Teacher's instructions
Measuring the voltage of three Daniell cells connected in parallel
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 6 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 the copper electrodes together using experiment cables with crocodile clips and then connect the last one
to the meter.
6. As described in step 5, connect the zinc electrodes together then connect them to the meter.
7. 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 parallel circuit, the measured voltage with three electrodes connected together should be V= 1.06 V approx. It can be seen that
connecting the electrodes in parallel does not lead to any increase in the voltage. What does increase in this case is the current as can
be measured using a multimeter.
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.