| time
requ.: |
10 minutes. |
|
objective: |
Demonstration
of oxygen as an air component. |
| material: |
- test tube d~18mm
- stopper
- ruler
|
- beaker 600ml
- burner
- powder spatula
|
|
chemicals: |
|
|
procedure: |
Insert iron powder into the test tube about 1cm high, close it with
stopper. Measure hight sA of the test tube from powder
surfacte to inner stopper end. While heating the iron powder keep thumb
pressing the stopper. Shake constantly while heating until powder
changes colour to black.
Let the test tube cool down while still pressing the stopper. Then put
the opening with stopper under water and remove stopper. Measure water
hight sW in the test tube. |
|
observation: |
Grey iron
powder changes its colour to black. After removing stopper water rises
in the test tube to a certain hight. |
|
interpretation: |
Iron reacts
with almost all oxigen from the air to iron(II)-oxide:
2 Fe + O2 --> 2 FeO |
|
calculation: |
Calculate the
proportion of water hight and former air hight in the test tube! sW:sA=.....:.....
|
|
result: |
In air we have
about 20% oxigen (this experiment provides between 17.5
and 22%). |
|
disposal of: |
Decant water
into sink, iron oxide to garbage bin. |
| note: |
It is
important to keep the stopper airtight on the test tube. |
| Quelle: |
G. Ströhla, University of Bayreuth.
|
