| time
requ.: |
10 minutes. |
|
objective: |
Demonstration
of the formation of an accumulator (secondary cell) |
| material: |
- beaker 150ml or U-tube
- multimeter
- 4.5 volt battery or DC power supply
|
- 2 graphite electrodes
- cables
- crocodile clamps
- electrode support
|
| chemicals: |
- zinc bromide solution
w~2%
|
|
|
procedure 1: |
Fill the
zinc bromide solution in the beaker, fix two graphite electrodes, measure
the voltage. |
|
observation 1: |
U = 0V |
|
interpretation 1: |
No
electrochemical cell. |
|
procedure 2: |
Connect the
battery to the electrodes. Wait for a few minutes. |
|
observation 2: |
Grey zinc
crystals and brown bromide solution appear. |
|
interpretation 2: |
Electrolysis
produces zinc metal through reduction and bromine through oxidation. |
|
procedure 3: |
Take the
battery away, connect the electrodes with the multimeter, measure the
voltage. |
|
observation 3: |
U ~ 1V |
|
interpretation 3: |
Electrolysis
has produced two electrochemical elements: Zn/Zn2+ and
Br-/Br2. Connected to each other an
electrochemical cell is obtained. The cell may be charged and discharged,
thus it is a secondary cell. |
|
disposal of: |
Fill the zinc
bromide solution into a flask, add some zinc powder and use again. |
|
source: |
from Barke, H.-D. et al.: One Hundred
Chemistry-Experiments to Avoid Chalk and Talk; University of Muenster,
2004. |
