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Fizzing Reactions

Primary schoolChemistryOne-to-one bicarbonate and acetic-acid stoichiometry, prescribed gas generation and an ideal gas in a balloon with a linear pressure-volume stiffness

Fit the balloon, tip the baking soda into vinegar and measure the gas. Remove the balloon in a fresh trial to let gas escape.

3D

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Measurement notebook

Change the setup, test a prediction and save the result. Up to 12 snapshots are kept.

About this experiment

Fit a balloon to a vinegar vessel, tip in baking soda and observe the gas collector inflate. Change reactant amounts to identify the limiting reagent, then compare a soft and a stiff balloon. An open-vessel trial connects the same chemical gas generation to material escaping instead of being retained.

Learning goals

  • Predict the limiting amount of bicarbonate or acetic acid.
  • Relate balloon size to gas amount and pressure rather than to bubbles alone.
  • Compare retained gas with gas that crosses an open boundary.

How to use it

  1. 1Fit the balloon, tip in the default powder and record the final gas volume.
  2. 2Increase baking soda while keeping vinegar unchanged and find the gas-production plateau.
  3. 3Keep the chemical amounts fixed, increase balloon stiffness and compare pressure with volume.
  4. 4Remove the balloon in a fresh trial, repeat the reaction and inspect escaped gas mass.

The model

One-to-one limiting amount
Coupled ideal-gas and balloon-compliance equation

Assumptions

  • The ideal reaction is NaHCO₃ + CH₃COOH → CH₃COONa + H₂O + CO₂. Vinegar density is 1 g/mL and its selected strength is acetic-acid mass percent.
  • Gas generation approaches the limiting amount as 1 minus exp(-0.07t), at fixed 298.15 K. Dissolved CO₂, acetic-acid equilibrium and changes of temperature are excluded.
  • An attached collector retains ideal CO₂ with absolute pressure P = 101.325 kPa + K times gas volume in litres. This positive linear stiffness is a teaching compliance law, not a real latex-balloon constitutive model. A detached collector retains no gas.

Try this in class

  1. Q1Why can extra baking soda stop increasing balloon size?
  2. Q2Why does a stiffer balloon contain the same amount of gas at a smaller volume?

Frequently asked questions

Does the balloon volume equal the ambient-pressure ideal-gas volume?

Only at zero selected stiffness. At positive stiffness the gas pressure is higher and its volume is smaller.

Why does the open vessel lose mass while the fitted balloon does not?

In the open case carbon dioxide leaves the measured system. In the closed case the collector remains inside that system boundary.