.
.
.
14. Hofmann alternatives 2 and 3: Plastic
Eppendorf pipettes and hypodermic needles
Eppendorf plastic pipettes
can be pierced by hypodermic needles. Their plastic ends are closed by welding.
So they are useful electrodes.
Photo 1 and 2: 3.5 mL measuring
Eppendorfs are pierced at their lower ends, the smaller ones at their upper
ones.
What you
will need
Three 3.5 mL
measuring Eppendorf plastic pipettes, one small Eppendorf, 6 hypodermic needles,
9-Volt battery, two connecting wires with crocodile clips, wellplate 6 (Zhou),
sodium sulfate solution, solution for air bubbles. Matches.
Experiment
Set the electrolysis
apparatus like shown in photos 1, 2, 3.
Photo 4: Lit
the gas bubbles in the wellplate 6 like shown in photo.
Observations
1. Photo 1,
2 and 3: Gas bubbles at both electrodes. After 2 minutes the electrolyte
is completely replaced by the gases formed in electrolysis.
2. Photo 1:
Nach 2 Minuten ist der Elektrolyt vollständig von dem gebildeten Gas
verdrängt. Es kann in Seifenlösung übertragen und entzündet
werden.
3. Photo 2:
Gas bubbles at both electrodes. Around the cathode the colour of the electrolyte
changes to green, around the anode it turns red.
3. Photo 4:
The gas bubbles explode.
Explanations: Red: 4 H2O(l) + 4 e- --> 2 H2(g)
+ 4 OH-(aq)
..........................Ox:
2 H 2O(l) --> O2(g) + 4 H+(aq)
+ 4 e -
Redox:
6 H 2O(l) --> 2 H2 (g) + O2
(g) + 4 OH-(aq)
+ 4 H+(aq)
contact Hugerat........contact Zhou.,,.contact Schwarz.............back......first publication: 19.04.2003.....last modification:
02.03.2007