Mercury drop pulsates when it is touched with an iron nail
name: Mercury surface tension changes in the mercury oxidation reaction
Wear lab goggles and gloves. Mercury vapours are very toxic! This experiment must be performed in a fume hood.
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Pulsation of the mercury drop is due a change of the surface tension. In the acid solution mercury is oxidized, and surface tension decreases. Mercury drop contacts with iron nail, and iron reduces the mercury ions to mercury metal because it has a sufficiently negative electrochemical potential. Surface tension of mercury increases, and the drop shrinks. Thus the contact of mercury and iron is broken and this oscillation cycle repeats.