Tuesday, December 4, 2012

Chemical Reactions Demonstration

We did three chemical reaction in class on Friday.  But before we get into those we need to to know what a chemical reaction is.  A chemical reaction is when the chemical bonds between two reactants are broken and and yields either a new compound or separate compounds.  Sometimes a catalyst is needed.  A catalyst is an entity that either helps start the chemical reaction or takes a small role in the reaction.

Our first demonstration was combustion.  A bottle was filled with the vapors from ethanol.  When the bottle was opened oxygen was added. My hypothesis was that the ethanol gases would ignite when introduced to our catalyst, fire.

CH3CH2OH + O2 ->  CO2 + H2O

I was right but something happened that I didn’t expect.  The fire and gases rushed out of the small spout from the bottle and propelled the bottle forward trailing fire.  Our end product was heat, carbon dioxide and water.

Our second demonstration was double replacement by adding baking soda to vinegar.  My hypothesis was that it would bubble.

CH3COOH + NaHCO3 -> H2O + NaOCOCH3 + CO2

When the baking soda and vinegar were mixed it created a gas.  When the gas was presented to a flame it snuffed the flames out.  The gas took the place of the oxygen which fed the flames.

Our next demonstration was single replacement by adding zinc to hydrochloric acid. My hypothesis was that it would begin to melt the zinc.

HC + Zn -> H + ClZn

When the zinc was dropped into the hydrochloric acid it began to bubble and gases appeared.  We then lit the gases on fire.  The hydrochloric acid/zinc mixture also caught fire and it began to turn grey/black.  Our product was hydrogen and chlorine zinc.

Our last demonstration was an example of decomposition.  W mixed hydrogen peroxide and potassium iodine together. My hypothesis was that it would bubble and the potassium iodine would remain a liquid.

H2O2 + KI -> H2O + O2 + KI

We added soap so we could see the reaction better and it created “Elephant Toothpaste”.  A foamy substance as well as gas.

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