Saturday, March 11, 2006
Chemical reaction 2 : thunderbolt under the water
Careful : around 100°C , Mn2O7 oxidize in explosive way organic substances ; for this reason you must prevent an overheating of the system .
Tools : 2 test tubes ( 16 x 160 mm ) , 2 supports whith clamps , becher 200 ml , pneumatic bath , glasses , gloves .
Reagents : KMnO4 , H2SO4 conc , ethanol
Experiment : the test tubes are fixed to the supports so as them are dipped in the water bath for about an half .Pour H2SO4 conc in the test tubes for about 2 cm height , then pour 4 cm of ethanol above the acid , avoiding the blending of the 2 fase .Now introduce in each tube a small cristal of KMnO4 , after a while , at the level of the liquids interface , are noticed yellow flash , which develops crackling .It seems that the flashes are produced under the water .
Gradually the mixture goes to green and brown .The experiment can go on for 15 min , during thath time the frequency of the flashes it's unpredictable .
Enlightenment : KMnO4 reacts first with the sulfuric acid to give Mn2O7 , that oxidize the alcol in a violent reaction .
2 KMnO4 + H2SO4 ------- K2SO4 + Mn2O7 + H2O
Mn2O7 ------- 2 MnO2 + 1/2 O2
Treatment : after cooling , neutralize with Ca(OH)2 and pour it in the inorganic salts waste .The water solution can be poured out in the sink .
