Limiting reactant demonstration (1)

MATERIALS

•       Cotton Balls
•       Gun cotton  (nitrated cellulose)
•       Large watch glass or crystallization dish
•       Long bbq lighter
•       Squirt bottle full of water
   

PRESENTATION

-      Place a cotton ball onto the watch glass and light with a lighter.  Do this twice. 

-      Place a similarly sized piece of gun cotton on the watch glass and light with a lighter.

DISCUSSION

-      Igniting the cotton ball (a fuel) at about STP, there is an incomplete combustion.  There is smoke emitted and residue left behind.  The limiting reactant in this case is oxygen. 

-      Ignition of the gun cotton produces a bright yellow flash with no smoke and no residue (if made properly and not aged).  This shows the effect of having essentially no limiting reactants.

A little history of nitrocellulose can be included with this demonstration (why movie film reels used to burn up, decompose, etc.)

HAZARDS

Nitrocellulose combusts somewhat rapidly although not explosively @ STP. Do not use a piece larger than the size of a cotton ball and start with a piece considerably smaller to gauge it’s performance.