Start with a Bang! Isopropyl Alcohol Exothermic Combustion Demonstration
Lesson 1 of 5
Objective: Students observe an exothermic combustion reaction to increase interest and awareness in science.
This lesson is based on California's Middle School Integrated Model of NGSS.
NGSS Performance Expectation (PE): (MS-PS1-2) Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occured.
Science and Engineering Practice 8: Obtaining, evaluating, and communicating information
Disciplinary Core Ideas (DCI): (PS1.B: Chemical Reactions) - Substances react chemically in characteristic ways.
Crosscutting Concepts (CCC): (Energy and Matter) - The transfer of energy can be tracked as energy flows through a designated or natural system.
This simple chemical reaction is designed to influence and excite students about science and chemistry. Your students will observe a simple exothermic combustion reaction and form opinions about what a chemical reaction is (MS-PS1-2). I have found that the right mood and theatrical presentation will go a long way towards bringing eighth graders to "your side".
This is a first day activity. Many teachers use this day to establish classroom norms and procedures. I take a different approach. Once the kids are excited about my class the norms and procedures are easier to discuss and later enforce after this demonstration.
Materials needed - isopropyl alcohol (rubbing alcohol), small beaker or measuring cup, 5 gallon water cooler bottle (empty), matches.
NOTE: isopropyl alcohol (rubbing alcohol) is sold at any grocery/drug store. It is commonly sold under many percentages. I try to purchase the higher percentage (70%) but I have done this demonstration with lower percentages and have had similar results.
Directions - pour approximately 50 mL of isopropyl alcohol (rubbing alcohol) into an empty 5 gallon water cooler bottle, swirl the isopropyl alcohol around in the bottle until it has evaporated, set on a table, drop a lit match into the bottle and stand back.
What to expect - the vaporized isopropyl alcohol will ignite in a combustion reaction, producing a small amount of heat, a flash of flame, and a swooshing sound. You may want to emphasize that repeating this reaction with the same measurements and procedures will produce an identical predictable result (DCI - PS1.B: Chemical Reactions).
I perform this demonstration on the first day of school, before I have taken roll. I let the kids walk in and pick their seats. At this point I try to say as little as possible to heighten the tension in the room. After the bell has rung, I walk over to my counter and hold up the Sparklets bottle for the kids to see (I try to be very theatrical about all this).
Keep in mind that some of the more adventurous kids are going to want to go home and try this in their backyard. To eliminate this danger, I only refer to the alcohol as 'isopropyl alcohol' and NEVER mention that it is ordinary rubbing alcohol that can be purchased at any grocery store. When students ask where they can buy isopropyl alcohol I reply that the "school buys it at a chemical store" (be vague). This is also a good chance to pick out your pyromaniacs that you may need to keep an eye on.
I put down the 5 gallon water cooler bottle and put on my lab coat, safety goggles, and remove any jewelry (always demonstrate proper safety). I then hold up a small beaker filled with about 30 mL [check amount] of isopropyl alcohol with an identifying label and a box of matches. Let the tension build in the room - don't say anything. At this point the room should be VERY quiet.
Knowing the type of kids that typically gravitate towards the back of the room, I purposefully place the water bottle on one of the back student tables. I carefully pour the isopropyl alcohol into the bottle and begin swirling around, humming to myself as I do it.
I then turn off the lights and light the match. The tension should be VERY thick by now. The next part is really fun. I turn to the nearest students and say, "Are you sure you want to sit this close?" There is typically a mad scrabble to move away from this table.
I then drop the match in and let the reaction commence. You should see a flash of light and a loud swooshing sound. There is also a loud reaction from the kids as the tension in the room is released.
The room should be filled with nervous laughter. I point out to the kids that they saw an exothermic (releases heat) chemical reaction. I also tell them that there are many types of chemical reactions and that they just witnessed a combustion (fuel, O2, spark) type reaction. I let them know that this is the sort of science they will be learning this year.
The student's job in this demonstration is to observe and obtain data (mental observation) of the nature of chemical reactions (Science & Engineering Practice 8: Obtaining, evaluating, and communicating information.) I like to point out that they may have observed light, heat, sound waves, and a transfer of energy. It is important to build a foundation for future science courses and mention a overarching science theme that energy flows from one source to another, in this demonstration energy flowed from the isopropyl alcohol (reactant) into carbon dioxide and water (products). (CCC - Energy and Matter).
The chemical reaction is:
2(CH3)2CHOH + 9O2 -> 6CO2 + 8H2O
Isopropyl alcohol + oxygen produces carbon dioxide + water
TIP: I always like to point out the small amount of water that now sloshes at the bottom of the water bottle that was not there before the reaction. At this point I wouldn't reference the above chemical formula. Many students may find this intimidating and decide that science is not for them - keep it fun!
If you would like to follow up this demonstration with instruction, I have included two PowerPoints. One designed to teach the difference between exothermic (release heat) and endothermic reactions (absorb heat)
The other one teaches the different types of chemical reactions.
I also created a mnemonic sentence for remembering the types of chemical reactions.
Squids don't carry roses.
S - synthesis
C - combustion
R - replacement