Department of Chemistry and Biochemistry Outreach Program

Station 2: Combustion

Station 1: Dry Ice Experiments

Station 2: Combustion

Station 3: Liquid Nitrogen

Station 4: Alloys

Station 5: Chemical Reactions

1. Methane Bubbles

1. Hand out some small bubble solution containers.  Have several students blow some bubbles by blowing into a wand and watch the bubbles float down to the ground.

2. Methane gas is commonly used as fuel for heating homes and for cooking.   Will methane gas bubbles rise or fall?  Blow some methane bubbles to see what happens.  Clean funnel with water if bubbles pop too easily.

3. What else can we do with methane bubbles?  We can light them!!!
Use a torch, a metal rod with a candle hooked to the end, to light the methane bubbles.  Use a big candle to light the small candle (using the big candle is easier than matches to re-light the candle).

SAFETY:  Students must hold the torch up above the funnel but not too close to the person making the bubbles and not too close to the funnel.  If the funnel accidentally catches fire there is no danger.  Simply hold the funnel away from you and away from the students and turn off the gas.

4. Light another bubble and ask students what they see?  What happens as the gas burns?  Do you see how the gas rises and spreads out as it rises?  The flame is showing you where the gas is.  What color is the flame?

5. Can you feel the heat given off as the methane burns.  The methane burns in air.  What gas in air does methane need to burn? 
Methane needs oxygen to burn.

           CH4 +  2 O2      →       CO2      +   2 H2O     +       heat  + light
      methane    oxygen            carbon           water                   fire
NOTE:  If the bubbles break too easily, turn off the gas and rinse and dry the funnel.

If there are two volunteers, one volunteer cleans up the methane bubble station while the other volunteer does the burning of the alcohol.

2. Burning a dollar bill

Solution:  50 mL of isopropyl alcohol, 50 mL DI water, 1-2 g NaCl  This makes 50% isopropyl alcohol.  The 70% isopropyl alcohol available in drugstores must be diluted. If you use the 70% alcohol the dollar bill will catch fire.

You have just learned about the combustion of methane gas.  There are many things that can burn.  Trees burn, paper burns, even liquids burn.  Alcohols are liquids that burn.  Will a dollar bill burn? 

1. Place a Bunsen burner between the jar of 50% isopropyl alcohol and the sink.

2. Light the Bunsen burner.

3. Soak a dollar bill in 50% isopropyl alcohol.  Remove it using tongs (grab the dollar bill in center, hold it in horizontal position).  Move the dollar bill into the flame of the Bunsen burner.  Leave it in the flame for only a second than take it out of the flame and watch it burn over the sink.

NOTE:  If the dollar bill itself catches fire, go to the sink and run water over it.  

Alcohol burns and the dollar bill is fine.  Why? 
What is the $1 made of?  

Paper.  Where does paper come from?  Trees.  Strong bonds hold paper together.

Alcohol molecules do not hold onto each other so strongly (note the high vapor pressures of alcohol at room temperature and pressure, you can smell it).  Alcohol burns at a much lower temperature than the paper so the paper does not catch fire.

Burning the alcohol produces CO2 and H2O just like when we burn methane or when we burn up sugar or carbohydrates - to burn anything containing C, H and O we need O2 and the combustion reaction produces CO2 and H2O.  So we breathe in O2, burn up food and breathe out CO2

Why is it better to use 50% then 70% isopropyl alcohol?  The 50% alcohol contains more water, water does not burn and keeps the $1 from burning while the alcohol burns.  

What is the purpose of adding the NaCl?  Sodium atoms heated in a flame emit yellow light so the flame is more visible if you add some salt to the 50% isopropyl alcohol solution.

Is a dollar bill made of special paper? Does this experiment work with a paper towel?

Fold up a paper towel, using tongs to hold the paper towel, soak it in 50% isopropyl alcohol.  Remove the paper towel, light it using a Bunsen burner by putting it into the flame for only a second than take it out of the flame to see it burn over the sink.   

Is there a difference between burning the $1 bill soaked in alcohol and the burning paper towel soaked in alcohol?  The paper towel burns much longer - why? 

If you were to spill water on the counter what would you use to wipe it up a dollar bill or a paper towel?  Why?  The paper towel absorbs more water.  A paper towel burns longer because it absorbs more alcohol than the dollar bill.  

SAFETY:  If there are two volunteers, one volunteer cleans up this station while the other volunteer does the burning of methane bubbles.  It is important to keep the counters clean.  Too much alcohol on the counter can catch fire.  If the counter does accidentally catch fire there is no great danger.  The alcohol burns at a low temperature and burns off very quickly.  Simply turn off the gas, step back and wait a second for the alcohol to burn off.