MadSci Network: Chemistry

Re: Chemical composition of the clear, colorless sphere of sodium

Date: Thu Feb 26 18:57:36 1998
Posted By: Jeremy Starr, Grad Student, Chemistry, California Institute of Technology
Area of science: Chemistry
ID: 886693730.Ch

Hi David,

	When sodium metal reacts with water, the following reaction is taking

	2Na(s) + 2H2O(l) ---> 2Na+(aq) + 2OH-(aq) + H2(g) + energy

Most of the energy of the reaction is released as heat. The hydrogen gas is
flammable and the reaction is hot enough to ignite the hydrogen upon
contact with oxygen (air). That is the source of the fire that occurs
during the reaction. Sodium metal melts at 97.8C (approx. the boiling point
of water) and has a density of 0.968 which is less than the density of
water. So, the reaction produces enough heat to melt the sodium before it
has completely reacted and the ball (or droplet) of melted sodium then
floats on the surface of the water until it has completely reacted. This is
the "clear, colorless sphere" you saw. In fact, the sphere is neither
clear, nor colorless. It is just highly reflective because the
imperfections of the mottled grey surface of solid sodium have been melted

_Safety Note_: Reacting sodium metal with anything is very dangerous!
Neither normal fire extinguishers nor most chemical fire extinguishers will
adequately extinguish an alkali metal fire. In fact some will make it
worse! (CO2 also reacts with sodium though not as violently as water does)
Be sure to have a big bucket of sand around when using sodium because it is
the safest way to extinguish a sodium fire. 

Hope this info was helpful.


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