Microscale Chemistry Experimentation for Teachers
Electric conductivity and electrochemistry of water samples with iron electrodes
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Electric conductivity and electrochemistry of water samples with iron electrodes
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Left
photo: Electric conductivity of different samples of water is being
compared using an AC/DC transformer at 4.5 V DC,
two
paper clip electrodes, and a multimeter. Distilled water gives 0.1 mA,
fresh water 1 mA and sea water 60.2 mA.
Photo
2: In salt water a green precipitation appears at the positive
electrode.
Two
drops of universal indicator solution (UI) are mixed with micro drops
of electrolyte around the left (-) and the right (+) electrode resulting
in a blue and a red colour.
Explanation
of the cathode reaction: 2 H2O + 2e- -------red---->
2 OH-(aq) + H2 (g)
Explanation
of the anode reaction:
Fe ----------ox----> Fe2+(aq) + 2e-In this case the
Fe of the electrode reacted (In experiment 8
the Fe will be replaced by an anode of C).Photo 3: Mixing
the electrolyte results in the formation of more green precipitate.
Explanation
of the precipitation reaction: Fe2+(aq)
+ 2 OH-(aq) -----> Fe(OH)2(aq)
Right
photo: Two drops of this green precipitate (1) were taken to the left
side of the container.
Drop 2 was mixed with a drop of hydrogen peroxide solution resulting in
a colour change from green to brown:
Fe(OH)2(aq) was oxidized resulting in brown Fe(OH)3(aq).
I