https://www.youtube.com/watch?v=zbmLMm2Mpa8
i'm no chemist but if i have to explain, when the piece of sodium hits the water/fenolftaleine mix it gets coated in it and reacts with it, cause it to bubble up and lift. the only reason it doesn't explode all over the room is gasoline being inflammable fuel.
also, something about small volcanoes.
I'm a chemist, so let's try to give a better explanation:
Sodium is a very reactive element because it only has 1 electron in its outer shell. Sodium wants to lose said electron to fullfill the '
octet rule'.
The reaction that occurs can be written as:
2Na(s) + 2H2O(l) --> 2Na+(aq) + 2OH-(aq) + H2(g)
2Na+(aq) + 2OH-(aq) <-> 2NaOH
The fenolftaleine is used as an indicator. Indicators change colors when the pH of the solution changes. Fenolftalein turns pink in basic solutions (solutions containing the hydroxide ion, OH
-), as can be seen in the video.
This reaction is quite exothermic, meaning it produces heat. If the reaction would have been executed without the gasoline on top, the hydrogen would have mixed with oxygen from the air, creating a gas mixture known as '
knallgas', which is very unstable. The heat from the reaction would have ignited the knallgas, triggering the following reaction:
2H2(g) + O2(g) --> 2H2O(g)
This reaction is very violent, creating a small explosion. To avoid this, we have to add a non-reactive solution which is lighter than water on top. Gasoline does fine in this case, though ordinary cooking oil probably would have been just as good.
One thing to consider though: If we would have bubbled oxygen into the bottom of the reaction tube, the knallgas could explode inside the tube. Even worse; the gasoline could be ignited by the first reaction!
The piece of metal 'jumps' because of the small bubbles of hydrogen being formed in the reaction. The bubbles attach to the metal and lift it to the surface of the gasoline.
:)
