| time
requ.: |
10 minutes. |
|
objective: |
Rusting,
corrosion. |
| material: |
- test tubes d=18cm
- stand, 2 clamps
|
- beaker 400ml
- beaker 100ml
|
| chemicals: |
- iron wool
- tap water
- strip of pure zinc
- strip of copper
|
- sulfuric acid
c=0.5-1mol/l
|
|
procedure 1: |
Place a dry
ball of iron wool in a test tube and a moistened one of the same size in a second test
tube. Close their openings by sinking them upside down in the large beaker with
water. |
|
observation 1: |
The water
rises in the second one. |
|
interpretation: |
Moisture is
necessary for rusting. Oxigen is missing from air because of its
reaction with iron to rust. |
|
procedure 2: |
Fix a strip of
zinc in the small beaker half filled with sulfuric acid. |
|
observation 2: |
There is no
reaction to be observed. |
|
interpretation 2: |
Zink kations prohibit hydrogen kations from
discharging. |
|
procedure 3: |
Touch the strip
of zinc with a piece of copper. |
|
observation 3: |
Gas bubbles
are coming from the surface of copper. |
|
interpretation 3: |
The gas bubbles contain hydrogen. Electrons can move
from zinc to copper, so hydrogen kations may be discharged at the copper
surface and will not be repelled by zinc kations. Copper acts as a
catalyst.
[Cu]
Zn + H2SO4
-----> H2(g)
+ Zn2+(aq) + SO42-(aq)
zinc diluted sulphuric acid hydrogen
zinc sulfate |
|
disposal of: |
Very low
concentration of zinc sulfate: sink. Reuse Zn, Cu. |
|
source: |
from Barke, H.-D. et al.: One Hundred
Chemistry-Experiments to Avoid Chalk and Talk; University of Muenster,
2004. |
