Mark's Discrepant Event 2 - CO2 doesn't burn
Author: Mark Yaney
Scientific Principles Illustrated:
Chemical Reactions
Combustion
Solutions
NGSS:
HS PS1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
Clarification Statement: Emphasis is on student reasoning that focuses on the number and energy of collisions between molecules.
Assessment Boundary: Assessment is limited to simple reactions in which there are only two reactants; evidence from temperature, concentration, and rate data; and qualitative relationships between rate and temperature.
Due to the chemical reaction between vinegar and baking soda, CO2 is released, and is held captive in the basin (the pitcher) since it is heavier than the surrounding air. When poured out onto the candle flame, the candle's combustion reaction is halted since the reactant, oxygen is diluted with CO2. The flame goes out because of an invisible gas. Magic? All you need is a few household items...
Materials
All that's necessary are the items pictured above, baking soda, vinegar and an open flame. If you're going to record it, you will need a camera and a cat to be curious around your feet while filming.
Leading Questions
Is there anything else in the pitcher besides the liquid you see? What happened to all the air in the bubbles that came out of the mixture? What do you get when you mix baking soda and vinegar?
Common Misconceptions
Many students who don't question the world around them -- including my current set of traumatized at-risk youth -- believe air is nothing, that it contains no matter, and has no mass.
Explanation
As the CO2 is poured out of the vessel onto the open flame...
The atmospheric O2 is displaced, and unavailable for the combustion reaction, causing combustion to stop.