Plastic Syringe for Molarity Experiment (Jake Dickerman)
Author
Jake Dickerman - Grant College Prep & Digital Arts Magnet
Principles
This tool is useful for determining gases produced by a chemical reaction and collecting them.
Standards
HS-PS1-7.
Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
Materials needed
Plastic syringe
Balloon
Funnel
Baking Soda
Vinegar
Procedure
Mass the balloon
Mass approximately 5g of baking soda
Using a funnel, insert your baking soda into a balloon
Pull 50 mL of vinegar into a plastic syringe
CAREFULLY pull the balloon onto the plastic syringe
HOLD THE BALLOON
Push the plunger, pushing the vinegar into the syringe
(this is the hard part)
As the finishes, you will need to twist the balloon up the "needle" of the syringe, pushing the liquid up to the end of the needle
Pull the plunger back down, trying to collect as much of the vinegar as possible
If you pull any air into the syringe, carefully push it back into the balloon
Tie off the balloon
Mass the balloon
Subtract the initial mass of the balloon from the final mass of the balloon. This will give you the mass of the CO2 in the balloon
Divide your mass of CO2 by 44g/mol to get your moles of CO2
There is a 1:1 ratio of acetic acid to produced CO2, this means your moles of CO2 should equal your moles of acetic acid
Multiply your moles of acetic acid by 60 to find your grams of acetic acid
Vinegar has a density of approximately 1 g/ml, which means you should have approximately 50 grams of vinegar
Divide your grams of acetic acid by your grams of vinegar, multiply by 100.
If you have less than 5% acetic acid, SUE!!!!!
Explanation
The total reaction between acetic acid and baking soda is
NaHCO3 (s) + CH3COOH (aq) --> CO2 (g) + H2O (l) + Na+ (aq) + CH3COO- (aq)
Kids think that acetic acid and vinegar are the same thing, but vinegar is actually a mild solution (about 5%) of acetic acid.
This includes both a neutralization reaction and a decomposition reaction. The decomposition releases CO2 at a 1:1 ratio with acetic acid.
This reaction (and probably versions of this experiment) should be extremely familiar to kids, but what I like about this version is that it really improves on this experiment. I originally did the experiment as a mini stoichiometry lab using erlenmeyer flasks, one of my students came up with this method while we were discussing systemic errors in procedure. The mini-lab can be seen below:
Questions
Potassium Iodide, Yeast, and iron chloride are all catalysts for the decomposition of hydrogen peroxide into water and oxygen gas. How would you design an experiment to determine which was the best catalyst?
Why is it vital to remove all air from a syringe before injecting it into a patient?
What would occur if you held your thumb on a syringe containing water and then pulled the plunger down? Explain.
Everyday examples of the principles illustrated
Syringes are useful due to the ability to remove air from the syringe without necessarily removing the liquid. They are also wonderful as a tool to precisely measure quantities of liquids.
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