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

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

1. 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?

2. Why is it vital to remove all air from a syringe before injecting it into a patient?

3. 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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